I'm trying to install Ubuntu 8.04 on an old PPC G4 I just started messing with, and I'm not able to actually start the install. It will boot the CD just fine and I try the 'expert install video=ofonly' command (along with just install video=ofonly and install). It starts loading the kernel, then the screen changes to grey with black text, stating the following:

copying OF device tree..
Building DT strings...
Building dt structure...
device tree strings 0x022b0000 --> 0x22b0ac8
device tree struct 0x22b1000 --> 0x022c3000
Calling quiesce...
returning from prom_init
The screen will hang there for about 3 minutes, then the system reboots.

It is worth noting that I don't know the specs on the machine itself, and that while it did run OSX at some point, today it will not boot to that, either. When I try to boot from the HDD, I simply get the Apple logo, then nothing.