Today, January 31, is the last day users who want to upgrade to the final version of Windows 8 for the cheaper promotional price have to purchase their copy.

After January 31, the limited time, promotional $39.99 upgrade price will end. Starting February 1, the Windows 8 upgrade (from previous Windows home/consumer SKUs) will cost $119.99. The Windows 8 Pro upgrade will cost $199.99.

Currently, Microsoft is charging $39.99 for an upgrade license to Windows 8 Pro from Windows XP, Windows Vista, or Windows 7. The promotional price is for individuals and small businesses and is limited to five upgrade licenses per customer.

Those who have been testing Windows 8 preview builds also are eligible for the $39.99 upgrade price. And those running Windows on Macs are, as well.

While I believed Microsoft's guidance to Mac users was they would need to purchase the system builder version of Windows 8, it turns out this isn't necessarily the case.

Customers running a full version of Windows 7 (Windows 7 Full Packaged Product, or FPP) in a virtual machine environment that supports Windows 8 can buy the Windows 8 upgrade through electronic software download (ESD) or at retail and upgrade from Windows 7 to Windows 8. If you are using Parallels Desktop, there's step-by-step knowledge-base guidance as to how to upgrade to the final version of Windows 8 on Parallels' site.

Microsoft Program Manager Eric Ligman has a good Q&A with all the ins and outs on the soon-to-expire upgrade deal. And ZDNet's Ed Bott has a good frequently asked questions (FAQ) post about Windows 8 upgrades .

Starting February 1, Microsoft is launching a new Windows 8 promotion for students only. The Windows 8 student offer will allow students to purchase the Windows 8 Pro upgrade edition online via the Microsoft Store for $69.99 (ERP).