can't get rid of wallpaper--help!

I have a dual monitor system with a GeForce2 MX400 on one and a
GeForce2 Pro on the other. I set up two different desktop wallpapers
using the Nvidia display properties dialogue. Then I decided to
change them. Problem is, no matter what I do the left monitor picture
won't change. It's set to the name of the photo I want in the
properties box, but every time I reboot the computer it displays the
old picture instead (even though the properties box still displays the
name of the photo it SHOULD be showing me).

If I go to Windows' display properties it shows
"permonitorwallpaper0.bmp" and 'permonitorwallpaper2.bmp". I've tried
deleting both these files, but they re-create themselves every time I
reboot. If I change the wallpaper using Windows' display properties,
it changes fine but after a reboot it goes right back to that old
picture. How can I get rid of it once and for all?