Dream Scene brings you dynamic Desktops where you can place any movie as desktop wallpaper. The format is preferably in WMW or MPEG. If you are a windows ultimate user you can directly download from ultimate extras.
Also StarDocks DeskScapes are also free. This is an add-on to Dream Scene that brings dynamic wallpapers to vista Ultimate. Deskscape adds .DREAM Files that have dynamic non-video content.
So your windows will look more dynamic and exciting.
Fore more info see here