Commonly, our desktop wallpaper is quiescency, do you want an animated desktop wallpaper ?
Also, the flash files are quite beautiful and most of them are animated or controllable, but you can not use a flash file as the desktop wallpaper directly.
Now, by using Flash Desktop 2002, you can convert any flash file to the wallpaper easily !
More info:
hxxp://www.toplang.com/users/flashdesktop/