Hum, I think the program DisplayFusion works wonders with wallpapers. It's what I use, and changes it automatically after a while from a selected folder, or from an online database that selects images to use.
Dude, it doesn't take up much space at all. My comp doesn't even feel laggy with 6 desktops :]
And my comp sucks. alot. I don't even have a real graphics card. And cakoman, can i give you a screenie?
My 6 desktops are better than your 4 >:]
EDIT!: New updated screenie. Newer version he reuploaded.