Sorry, I forgot to mention. I'm using Ubuntu 9.10 (Karmic). I actually did search for it, but all of the websites said to do this:
1. Logout of your current session and return to the GDM
2. Switch to the tty command line prompt using Ctrl-Alt-F1
3. Login using your normal login/password
4. at the command line prompt type: export DISPLAY=:0.0
5. then type: sudo -u gdm gnome-control-center
6. Switch back to the gdm screen using Ctrl+ALT+F7
7. The gnome-control-center should be loaded. Use it to configure your GDM.
8. Click on the Appearances icon, in appearances you can change your GDM’s font, theme and background image.
9. Close the gnome-control-center and login normally.
I get a bunch of errors when I do the sudo -u gdm gnome-control-center. ( such as Can't load gtk-theme-selecter.desktop and Can't load gnome-cups-manager.desktop)
I also tried doing the instructions here:
but I don't see where I'm supposed to change the file (ie, I do sudo xsplash and I just get the default splash screen).