not much up on the mac, will this work???
For Apple Macintosh G3, G4, and G5 computers, including iBooks and
PowerBooks as well as IBM OpenPower machines.
cdimage.ubuntu.com/.../ubuntu-7.04-desktop-powe\
rpc.iso

from here..
http://cdimage.ubuntu.com/ports/releases/feisty/release/

and there are others for you to play with :)
www.ppcnerds.org/index.php

and FAQ too..
https://wiki.ubuntu.com/PowerPCFAQ