Microsoft and online retailers last week kicked off Windows 7 sales in the U.S., Canada and Japan, taking pre-orders at prices discounted by as much as 58% and zooming to the top of Amazon.com's sales.

The upgrade for Windows 7 Home Premium, priced at $49.99, immediately stormed to the top of Amazon.com's bestseller list. The $99.99 Windows 7 Professional Upgrade held the No. 2 spot in software, while Windows 7 Ultimate Upgrade, a $219.99 package that has not been discounted, claimed No. 4 as of Friday afternoon.

Microsoft officially announced the limited-time deal Thursday, although details had leaked earlier this month when the Engadget site published a Best Buy memo that spelled out the prices and start date.

The discounted prices are good from today through July 11 in the U.S. and Canada, or "until supplies last," Microsoft noted in fine print. Pre-order prices will cease after July 5 in Japan. Customers in the U.K., France and Germany will be offered similar pre-order discounts starting July 15.

Microsoft declined to get more specific than "until supplies last" when asked today what cap it has in mind for Windows 7 discounted pre-orders.

Prices, and the amount of the price cuts from Microsoft's suggest list, vary by country. In the U.S., Home Premium has been discounted 58%, while Professional has been reduced by 50%. Canadian users get a 50% discount on both editions, but Japanese customers receive a 53% discount on Home Premium and only 45% off Professional.

In the U.S., Windows 7 upgrades are available from Microsoft's own online store, as well as from Amazon.com, Best Buy, Frys, Newegg, Office Depot and Tiger Direct. Canadians can pre-order the OS from Microsoft, Amazon.com, Best Buy, Future Shop, London Drugs, Staples and The Source. Most are throwing in free shipping, and saying that they will deliver the operating system on Oct. 22, the date Microsoft has set for Windows 7's launch.

Only Microsoft's online store is taking orders for downloadable copies of the new operating system as well as shrink-wrapped editions. The company adds an additional $14.99 to the price if customers want a physical disc as well as the download, however.

According to Microsoft, the Windows 7 upgrades can be purchased and used by users currently running Windows Vista, Windows XP and the even-older Windows 2000. For the latter two operating systems, however, Windows 7 must be done as a "clean install" that deletes all data and applications; users must back up data before the move to Windows 7, then restore the data and resinstall all applications. Only Vista users can do an "in-place" installation that leaves data, Windows settings and applications intact.

Although some analysts have slammed Microsoft for setting Windows 7 Home Premium's upgrade at $120, they have applauded the pre-order discounts. "The $49 initial price is a nice reward for loyal customers," said Michael Gartenberg, an analyst with Interpret, in a blog post yesterday. "But the 'real' upgrade pricing is way off for what the market will likely bear, especially during these economic times."

This story, "Windows 7 Pre-Orders Dominates Amazon Sales" was originally published by Computerworld .