Upgrading an operating system install is never a small decision. Upgrading to Windows 8 is a particularly challenging decision because the user-interface has so substantially changed from what we were all used to in Windows 7. In this article, I'll give you some guidelines that -- based on your personal circumstances -- will help you decide what's right for you.

See Also: Dogfooding Windows 8: six long-term Windows 8 users tell all

If you don't have time to read all the details, you can skip to the end of the article and read a short summary of my recommendations.

Also, almost all your upgrading questions (licenses, copies of downloaded software, etc.) are answered in Ed Bott's excellent Everything you need to know about Windows 8 upgrades (FAQ part 2) . Be sure to read it and Ed's first installment, The ultimate Windows 8 upgrade FAQ .

Before January 31, 2013

Pricing is always an important component of any upgrade decision. Microsoft is offering a number of great upgrade deals for moving to Windows 8 Pro, but the deals expire on January 31, 2013.

What might be a good, cost effective decision before January 31, seems like a far less viable decision after. Right now, most existing Windows users can get Windows 8 Professional for $39.99 -- before January 31. Although Microsoft hasn't published their eventual Windows 8 Professional price, the best Windows 7 Pro upgrade price we've seen is in the $160 range. Essentially, you could buy four Windows 8 Pro upgrades now for the price of one copy after January 31.

So, if you're reading this in February or later, factor that into your decision.

Price options

So what are the pre-February 2013 price options? There are two that are worthy of consideration:

Windows 8 Pro upgrade for Windows 7, Vista, and XP users is $39.99. Here's Microsoft's upgrade page.

Windows 8 Pro upgrade for buyers of Windows 7 PCs is $14.99. Here's Microsoft's upgrade page.

These upgrade prices are only available for downloaded versions of Windows 8. If you want it on disk, you're spending at least sixty bucks.

If you're buying a new PC

If you're buying a new, off-the-shelf PC or laptop, you may have the option of having it equipped with Windows 8 or Windows 7. Unless you're absolutely in love with the Windows 8 experience, I recommend getting the system with Windows 7 installed and then, immediately taking advantage of the $14.99 Windows 8 upgrade offer. You don't have to install it right now, but you're not going to see a better price.

The reason I recommend this approach is because we've seen a number of problems with users deciding to "downgrade" their new Windows 8 consumer PCs to Windows 7. Drivers for Windows 7 may not be published by the PC vendors for newer PCs, and it might be a real challenge to back-rev to Windows 7 later if you want to.

Also, a license of Windows 7 (even the Home version) is considerably more expensive than the $14.99 upgrade option. So, for a new PC, you're better off getting Windows 7, and then immediately securing a cheap upgrade path to Windows 8.

If you're buying a new PC with a touch screen

If you're buying a new laptop or tablet-ish thing with a touch screen, you're probably going to want to just bite the bullet and go with Windows 8 directly. Windows 8 is optimized for touch.

That said, if there is the option to get your touch screen-enabled laptop with Windows 7, then my $14.99 upgrade recommendation from above still applies. It's still a smart idea to get Windows 7 now, because you're almost undoubtedly not going to be able to go back later and get drivers if you should change your mind and want Windows 7.

Next up, if you're building a new PC or are running XP...

If you're building a new PC

But what about if you're building a new PC from components? In most cases, those of us who build our own PCs need to individually buy our own operating system licenses. Further, to take advantage of the $14.99 upgrade sale, you have to supply an existing Windows 7 license code and retailer name, so an off-the-shelf OEM version of Windows 7 might not be eligible.

So, for this recommendation (and all the rest in this article), I'm assuming you're making the decision based on the $39.99 Windows 8 Pro upgrade offer. The other factor is that this $39.99 price is an upgrade. You're going to need to sacrifice an existing OS license to be able to perform the upgrade.

The fact is, no new PC should be running XP or Vista. XP is just too vulnerable and support is ending in 2014, and Vista is, well, Vista. So you should either install Windows 7 or Windows 8. Also, it's getting far harder to find workable XP drivers for new components, so you're pretty much forced to go with Windows 7 or later for production use.

From a cost point of view, one approach would be to recycle an old XP or Vista license on your new PC, get it installed to the point of basic operation, and then install the Windows 8 upgrade over it for forty bucks. That will get you a modern OS on your PC for a pretty inexpensive price.

On the other hand, your decision probably should be made more based on which drivers are available for the components you've chosen. Go to each vendor's driver download site and be sure there are drivers available. The OS with the better drivers is probably going to be your choice.

If you're running XP

This is perhaps the easiest recommendation, but even here, what you do depends on how you're using XP. I'll talk about the edge cases in a moment. For now, let's just discuss those legion of XP machines running around, open, and completely vulnerable on the Internet.

I'll put this quite simply: if you're running an XP machine and you're reading email or browsing the Web, you need to upgrade immediately. XP is enormously vulnerable to exploits, you can't run Internet Explorer later than IE8, and your PC is a calamity waiting to happen.

So you should upgrade to either Windows 7 or Windows 8. Period. Now, as it happens, it's probably actually a better choice to upgrade to Windows 8. First, again, you can get the Windows 8 Pro upgrade for only $39.99 and any Windows 7 upgrade will cost you more.

Second, as Jason Perlow reports , Windows 8 can breathe new life into old PCs and provide better performance and boot-up speed than Windows 7.

Essentially, upgrading an old PC from XP to Windows 8 will give your PC a new lease on life. Otherwise, you're probably living on borrowed time.

Now, what about those edge cases? What I'm talking about are old Windows XP machines that are single-use devices and don't browse the Internet. For example, I have an old server monitor that runs one piece of software -- a display of which servers are up or down -- and I think I rebooted it once, back in 2009 or so. For PCs running XP that are special use devices, I don't necessarily recommend upgrading. Especially since some of that special-use software might not run on Windows 8 (although you could run it in a Hyper-V XP-based virtual machine, another cool Windows 8 feature).

But, for every other XP user, I strongly recommend upgrading to Windows 8.

Oh, and as a shout-out to all of you gung-ho Linux kiddies, I will point out that my ZDNet colleague, Steven J. Vaughan-Nichols, colorfully claims Windows 8 belongs on older PCs like a fish needs a bicycle . He recommends installing a Linux distro. Of course, Steven pens the Linux and Open Source column, so take that into account when making your decision.

If you're running Windows 3.x, 95, 98, or Me

Seriously? You are seriously still running one of these antiques? First, Windows 8 won't upgrade one of these clunkers, and second, if you're still running something from the Cretaceous Period, you probably have your own twisted reason.

Frankly, if I were you, I'd rush down to my local store and buy anything else, but perhaps you're living in the Museum of Forgotten Toys. Anyway, I can't help you. Not sure if anyone can.

Next up, if you're running Vista, Windows 7, and my recommendation summary...

If you're running Windows Vista

I have one old PC sitting on a shelf that runs Windows Vista. It's sitting on a shelf since I haven't booted it for more than two years, but back in the day, it actually ran pretty well. Vista, once all the bugs got worked out, wasn't really a half-bad operating system, despite its reputation.

Vista is a bit of a way-station security-wise, between XP and Windows 7. While Vista does implement some of Windows 7's increased security, it's still far more vulnerable than a modern operating system. As with Windows XP, if you're actively using your Vista machine, you should upgrade to either Windows 7 or Windows 8 -- and Windows 8 is probably the better and more cost-effective choice.

If you're running Windows 7

Well, I'll tell you this: I'm not rushing out to upgrade my Windows 7 PCs. I am going to buy as many of those $39.99 licenses as Microsoft will allow, because I expect to upgrade my Windows 7 PCs eventually and that's the best Windows pro price I think we'll see for a long time.

I find that Windows generally runs fine for six to eighteen months, and then things start to get crufty. At that point, I generally do a fresh reinstall, and that cleans things up quite nicely.

I expect that, over time, I'll start bringing in a bunch of Windows 8 machines, upgrade some older boxes, and then, as each Windows 7 machine starts getting cranky, I'll throw a fresh coat of paint on it in the form of a Windows 8 upgrade. But that will be in the fullness of time, not this week.

As for you, here's what I recommend. I again recommend snarfing as many Windows 8 Pro licenses at $39.99 as you anticipate needing, because the price is very right. But I don't recommend upgrading your Windows 7 PCs unless you're enamored by the new Windows 8 experience (really?) or your PC is getting cranky enough that it's time to do an OS reinstall.

Basically, my bottom line for Windows 7 PCs is this: if you're installing the OS, install Windows 8. If you're not doing an install, if it ain't broke, don't fix it. But make sure you get the sale-priced Windows 8 license now, to fix it later.

Recommendation summary

All of these pertain to decisions made before January 31, 2013. Prices become more expensive after that. Here's a short summary of what I recommend:

If you're buying a new PC: If you can, buy it with Windows 7 and take advantage of the $14.99 Windows 8 upgrade offer to use later.

If you can, buy it with Windows 7 and take advantage of the $14.99 Windows 8 upgrade offer to use later. If you're buying a new PC with a touch screen: You may have to buy Windows 8 to take advantage of the touch screen.

You may have to buy Windows 8 to take advantage of the touch screen. If you're building a new PC: If you have a Windows 7 license, go ahead and use it if you wish. If not, use a sacrificial license to an older OS to install the Windows 8 Pro upgrade.

If you have a Windows 7 license, go ahead and use it if you wish. If not, use a sacrificial license to an older OS to install the Windows 8 Pro upgrade. If you're running XP: For security reasons, you should install a Windows 7 or Windows 8 upgrade just as soon as possible. Windows 8 Pro is cheaper, and will run better.

For security reasons, you should install a Windows 7 or Windows 8 upgrade just as soon as possible. Windows 8 Pro is cheaper, and will run better. If you're running Windows 3.x, 95, 98, or Me: Seek professional help.

Seek professional help. If you're running Windows Vista: You, too, should upgrade to Windows 7 or Windows 8, and once again, Windows 8 will be cheaper.

You, too, should upgrade to Windows 7 or Windows 8, and once again, Windows 8 will be cheaper. If you're running Windows 7 : If it ain't broke, don't fix it. When it's time to do an operating system reinstall, then consider Windows 8 (but buy it now, while it's on sale).

: If it ain't broke, don't fix it. When it's time to do an operating system reinstall, then consider Windows 8 (but buy it now, while it's on sale). If you're a Mac or Linux user: Stop yer laughing. It's not polite.

There you go. Don't forget to visit ZDNet's comprehensive Windows topic section for all the latest in Windows 8 news. And remember, Windows upgrades go best with pizza and the non-alcoholic beverage of your choice. Don't drink and install drivers.