We call the 12.1 G4 (the aluminum case 12.1) a P99 so bear with me. If you have a kernel panic on a P99 unit, before calling tech support because you can't get it fixed, check out the AirPort card if you have one -- it's located in the battery compartment. Make sure that it is seated properly. If it isn't, the loose card can cause kernel panics. Just a little FYI type thing for those who have this unit.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030828183927421