Amazon.com, which has begun taking pre-orders for Vista, also reveals list prices for two other versions. Those prices will be similar to what Microsoft currently charges for comparable versions of Windows XP, the current system.

According to Amazon.com's Web site, the version of Vista geared toward work use, Windows Vista Business, will cost $299, similar to the price for Windows XP Professional. The consumer version, Windows Vista Home Basic, will cost $199, the same as Windows XP Home.

But Microsoft is hoping most consumers will embrace Windows Vista Premium, which offers entertainment capabilities such as the ability to record live television. That version is listed at $239. Similar functionality is available in the Media Center edition of Windows XP, but that is only available pre-loaded onto a computer, so comparable pricing is not available.

The company also is hoping to sell consumers on another version of Vista, called Ultimate. That version, geared toward home users who also want to do some work from the family den, is listed for $399 on Amazon.com's Web site.

The prices listed on Amazon.com's Web site are for those users who choose to buy the operating system on its own. Many consumers, however, buy Windows as part of a new computer purchase.

Microsoft declined comment on the prices. Kevin Kutz, a director in Microsoft's Windows client unit, said the company will officially make prices public when it releases a near-final test version, called release candidate 1, which is expected by the end of September.

Amazon.com spokesman Sean Sundwall said the Seattle-based online retailer posted the listings and began taking pre-orders two or three weeks ago because consumers were asking for that option. He said the prices are from the latest price sheet that Microsoft provided.

"The one thing we were certain on is the price," Sundwall said.

But Sundwall said Amazon.com can't be certain when Vista will be released. The retailer lists the ship date as Jan. 30, which Sundwall said was an estimate based on Microsoft's public assertions that it plans to release the consumer version of Windows in January.

Kutz said Microsoft is still on track to deliver the much-delayed Vista to big business clients in November and to consumers in January. But he reiterated that the company will not hesitate to delay Vista's release if any problems crop up.

"Quality is the ultimate determinant," he said.

Goldman Sachs analyst Rick Sherlund, who was among the first to note the Amazon.com listings, said in a research note that the prices listed on the Web site, if accurate, could provide some boost to Microsoft's earnings. But he wrote that it was hard to judge exactly how Vista will impact Microsoft's earnings because details such as the exact release date aren't yet clear.