Well if you have vista ultimate you can use movies as backgrounds.. but you can now do it with non ultimate version as well just google DreamScene_EN
Make sure you backup your computer as I had it disable menus on me when I downloaded the wrong version make sure its the patched version(Version: 6.0.6000.16504) check readme.. with that version had no problems with 6 computers.. just install it following the insturctions (idiot proof) have to have vista sp1 installed and after that it works great... If you want free scenes look at dreamscene.org got alot of nice backgrounds... You have to have areo on to use this though so make sure you goto turn areo on..
C:\Windows\Web\Windows DreamScene
^
thats so they will show up in the dreamscene folder
heres an example
http://www.youtube.com/watch?v=kTjvl...rom=PL&index=8