Wallpaper issues

Okay,
This has been going on for a while now, but I've never really found the right place to ask, so I'll try here.
For some reason, something or someone has disabled the ability to change the wallpaper on my desktop. The list is 'greyed out' & unselectable, and the only thing you can change is the background colour.
Does anyone know if I am able to fix this?

I am on the admin account, & I'm running Windows XP Pro.
Thanks in advance for any information

you might wanna look up on changing registry settings,
you can google up some registry guides and look it up.

Well, I looked, & really the only thing I was able to find that deals with wallpapers is changing the position.
Would using the windows disk to repair work?

start -> run -> gpedit.msc[enter] and look in windows settings to see if it has been disabled

After doing a lot of things, I finally was able to find the right registry & delete it. Everything's working now.
Thanks for the replies.

>>1
That's one of the after-effects of getting infected with SpySheriff or one of its variants. Many anti-spyware packages don't remove it properly, and leave behind errant registry keys that break, among other things, your desktop wallpaper. Open regedit and go to the key HKLM\Software\Microsoft\Windows\CurrentVersion\policies\system\ and delete the \wallpaper\ key, then reboot.