Spaces and Backgrounds problem

[interpolarity]

I hope this is in the right place...

Whenever I try to change my background, it goes away when I switch spaces and doesn't come back. When I go back to System Preferences it looks as if I never changed the background...

Why is this and how can I fix it?

I have a Black MacBook (bought just before the aluminum upgrade) with 4GB of RAM, 250 GB of space, 30 being used for BootCamp, and 10.5.6 OS

Please and thank you

 

[interpolarity]

*oops*

 

[interpolarity]

Please help me out with this. I am tired of the space background...

I deleted ~/Library/Preferences/com.apple.desktop.plist and restarted, but it didn't work
I repaired disk permissions and it didn't work

Actually, the com.apple.desktop.plist file is being changed, but the background doesn't...

HELP!!!!!!!