In a keynote, chairman and chief software architect Bill Gates touted deals with hip brands including MTV and TiVo, and played up the sales momentum of Windows-based media-centric PCs and the Xbox gaming system.

Perhaps one of the most significant announcements was that Microsoft has signed up more than 50 partners to its PlaysForSure branding program, from online services to device makers.

The PlaysForSure program allows partners to put a mark on their products certifying interoperability with Microsoft’s digital rights management systems, important at a time when Apple’s proprietary dominance of digital audio is being increasingly criticized.

With TiVo, the greatly popular digital video recording service, Microsoft announced a relationship that will enable TiVo users to move their recorded TV shows to Windows-based Media Center PCs, Portable Media Centers, PocketPCs and Smartphones, using TiVo’s new TiVoToGo software.

Microsoft has sold 1.4 million Media Center PCs now, Gates said, doubling sales year-on-year. Xbox is expected to move 20 million units by July, with the Halo 2 game selling $125 million of copies in its opening weekend, he said. The company also said that 90 million copies of Windows Media Player 10 have been downloaded by users in the last three months.