The company also expanded the tester base of Vista to about 5 million users as it begins gearing up for Windows Vista's widespread release, scheduled for early next year.

Microsoft's suggested retail pricing is US$399 for Windows Vista Ultimate, $299 for Windows Vista Business, $239 for Windows Vista Home Premium and $199 for Windows Vista Home Basic.

Upgrades to Windows Vista from XP are $259 for Windows Vista Ultimate, $199 for Windows Vista Home Premium and $99 for Windows Vista Home Basic.

The prices are the same as the ones listed on Amazon.com's Web site last week, except the online retailer listed an upgrade for Vista Home Basic as $0.95 more. Amazon.com is already taking pre-orders for Vista, and lists on its Web site that the OS will be available on 30 January 2007.

Vista on horizon

Microsoft has not given a firm date for Vista's release, but is targeting sometime in January for the OS's general release. The company plans to release Vista to business customers in November.

On Friday Microsoft made available Release Candidate 1 (RC1) of Windows Vista, which means the OS is in its final testing phases. Windows Vista's release has been delayed several times, and industry and financial analysts have said they think the release will slip even further into 2007.

However, analysts Tuesday said the release of RC1 and Vista's pricing are positive signs the company could be on track to release the OS on time.