Microsoft wants to make sure consumers and small businesses know there are myriad ways they can acquire Windows Vista - particularly in premium versions - when it becomes generally available on 30 January.

Microsoft has announced in the US today that, for the first time, users will be able to purchase its Windows OS by downloading it over the internet.

Various consumer versions of Windows Vista - such as Windows Vista Home Basic, Windows Vista Home Premium and Windows Vista Ultimate - will be available on Microsoft's Windows Marketplace e-commerce site, said Bill Mannion, director of marketing for Windows. Microsoft Office 2007 also will be available on Windows Marketplace.

Microsoft has sold games, some of its less popular applications and partner software on Windows Marketplace, but it previously hasn't sold its core Windows and Office products there, Mannion said. The company revamped the site in August, adding a feature called Digital Locker, which keeps track of a customer's licence key online so that software can be downloaded and securely purchased over the internet. This feature is one of the reasons Microsoft now feels it's safe enough to distribute Windows Vista and Office over the internet, he said.

Microsoft has also made clear later that it's pushing hard for consumers to buy the premium versions of Vista - Home Premium and Ultimate.

Separately, the company is set to announce pricing for a previously revealed consumer upgrade system for Vista called Windows Anytime Upgrade. Microsoft has said it will put all of the versions of Vista on one DVD in packaged form, or on a PC if the OS comes preinstalled. Users will get a product activation key that can activate whatever edition of Vista they purchase, and then can use that to install the OS.

Finally, Microsoft is expected to unveil a promotion through 30 June intended to inspire computer enthusiasts with more than one PC in the home to upgrade more than one system to Vista.

The Windows Vista Family Discount allows a customer who buys the retail boxed version of Ultimate to purchase digital licences for Home Premium for $49 (£25) each that can be installed on up to two other PCs in the home, Mannion said. As mentioned before, the suggested retail price for Windows Home Premium is $159 (£80). No details of UK pricing have been announced.