Sales of Vista during the first month that the newest Windows operating system was available to consumers were more than double the sales that Windows XP racked up in twice the time, according to Microsoft.

Microsoft sold over 20 million Vista licenses in its first month, the company said. That compares to the first two months of XP sales, which reached 17 million licenses.

The figures didn't impress one expert. "I would be more surprised if that weren't true," said Richard Shim, an analyst with IDC. "Back when XP launched, the cards were really stacked against XP. We were just coming off the bubble bursting, and the PC market was in a trough."

In addition, there are a lot more PC users now than when XP launched, so Vista sales should naturally be better, he said.

The 20 million Vista licenses include software sold to PC makers, upgrades, and the full packaged product sold to retailers from January 30 to February 28, Microsoft said.

While Microsoft didn't break out Vista sales by version of the product, anecdotally, users appear to prefer the premium version. Dell customers are "overwhelmingly" choosing the premium version of XP, a Dell spokesman said in the Microsoft statement. IDC expected that because PC makers have been making more powerful machines in order to support the full Vista experience, and they're often selling such PCs without a price premium, Shim said. That's encouraging end-users to choose the more robust systems along with the premium version of Vista, he said.

The most important test for Vista, however, will come next year after enterprises have had the time to carefully examine whether or not to upgrade to Vista soon, Shim said. "The question is, does that [sales record] continue, and what happens when the commercial market begins to adopt," he said.