It would be harder to find a bigger fan of Windows 7 than Bill Veghte, the Microsoft senior vice president in charge of the company's PC Windows business. But even as he touted the advantages of the upcoming operating system this morning, Veghte cautioned analysts that Windows 7, like everything else, won't be immune to the difficult economy.

"I am incredibly optimistic about Windows 7 as a product. As you read the blogosphere, you read the competitive reviews ... we've got a great product," Veghte said at the UBS Global Technology & Services conference, via webcast. "But history would tell us that generally as you ship a new Windows release into the market, the bump that you get in terms of PC units is very modest."

Over the long term, the advances in Windows 7 will contribute to the PC growth rate, Veghte said. But in the short run, past Windows releases show that the product releases themselves impact PC growth rates "very, very modestly," he said.

UBS analyst Heather Bellini asked Veghte about the theory that a new WIndows version will persuade big companies to ugrade their hardware.

"In the conversations that I have with CIOs and IT folks, certainly there is very good enthusiasm about Windows 7 and the opportunity that affords," he said, citing improvements in security, manageability and user experience. "My personal opinion, though, is it will get drowned by the macroeconomic enviroment. As the macroeconomic environment comes back, people will have to buy PCs."

Another key measure for Microsoft is the Windows "premium mix" -- the number of high-end Windows licenses sold as a percentage of the overall number of Windows licenses. That number was 62 percent in Microsoft's most recent quarter -- down 14 percentage points from the same period a year ago. The premium mix was high in Vista's early days but has since dropped, largely because of the increasing popularity of low-cost netbook computers.

The current problem for Microsoft is that Windows XP has been the default operating system for netbooks, because they struggle under the weight of the beefy Windows Vista. In contrast, Windows 7 is expected to be much better on netbooks, but even so, Veghte downplayed the impact on Microsoft's business -- again citing the economy.

"In this economic environment, I think it’s very hard to see us back at the mix we had in the early days of Windows Vista," he said.