Earlier this week at the CES Microsoft announced some of their Ultimate Extras, this is a feature in the Ultimate Edition of Vista which periodically pulls down new applications as Microsoft release them. They announced three for launch on the 30th of January; Hold 'Em Poker Game, BitLocker and EFS Enhancements and the one I'm most interested in Windows DreamScene.
Video: Demo of Full Motion Desktop
Basically it allows you to use an MPEG2 or WMV as your desktop wallpaper. Microsoft ship both HD and standard resolution videos which seamlessly loop with the software too.