If you are looking for animated Windows Vista wallpaper or animated Windows Vista backgrounds, you should consider that only Windows Vista Ultimate has the ability to run the animated wallpapers which are named as Dreamscene in Windows Vista.

Dreamscene can be downloaded and installed on Windows Vista Ultimate edition from the Windows Vista Ultimate Extras. You can find the instructions on article titled How to Install Windows Vista Ultimate Extras

You can post links and resources where we can find and download animated backgrounds and wallpapers aka Dreamscene videos for Windows Vista in this forum post.

Here is the first link where you can download Windows Vista Dreamscene videos :
http://dream.wincustomize.com/
And www.winmatrix.com is a good resource for free dreamscene downloads.