This is sort of a long shot, but there's always the chance that someone has managed it. I just bought my wife a Mac mini. She has little use for Linux on it, but I'm always into playing with such things. For that matter, I have a dual G4 tower that I haven't bothered putting Linux on.
What I'd like to do is buy an external Firewire drive and put Debian on it such that I can plug it into any Mac (well, presumably only New World), have it come up as recognized in the Mac bootloader that comes up when one holds down Option, then chain load into something (yaboot, I expect) where I can pick an appropriate kernel (G3, G4, G5, SMP, whatever). This is sort of like a liveCD (with less autodetection), actually, but much more useful. I brought up the idea of booting off an external Firewire drive a couple of years ago, and no one had any good answers. Has that changed? Has anyone managed to do what I'm talking about? --Greg