For those who wish to change the default login splash background in fedora 14, the offending graphics are to be found in /usr/share/backgrounds/laughlin/default.
Step 1 is to add your preferred ping image alongside the laughlin.png in whichever directory your monitor uses. I am apparently "normalish" so I put my background there. 1280x1024 RGB.
Step 2 - edit the "laughlin.xml" file in the "default" directory, replacing "laughlin.png" with the name of the file you added above.
To get the proper dimensions for an image, you can load laughlin.png into the GIMP and read Image/Properties. While there, you could erase the contents of the image and replace with your own, similar to rinsing out your mouth. Then spit.
If you use a graphic from outside fedora, don't forget to run restorecon on the file, or else SELinux won't allow gdm to display it.