Windows DreamScene is a utility that allows users to set WMV/MPG format videos as desktop wallpaper. It is available for Windows Vista but has been dropped in Windows 7. As a Windows 7 user, do you need the DreamScene feature of Windows Vista Ultimate?
If so, you should give DreamScene Activator a shot, which is a freeware that allows you to activate DreamScene for Windows Vista & Windows 7.
Once you have downloaded DreamScene Activator, then run it as administrator. By clicking on the Enable DreamScene button and restarting Windows Explorer, you will enable DreamScene feature in Windows 7.
When you want to set any video in WMV/MPG format as desktop wallpaper, just right click on it and select Set as DreamScene.