Why won't ubuntu work?
Thanks for the help so far, here's what's happened:
I downloaded 'ubuntu-9.10-desktop-powerpc.iso' from the link given by David. I was surprised to find it was 705.3MB (5.3MB too big for a CD) so I followed the instructions on the site word by word but used a DVD instead, Disk Utility says: 'could not be completed'.
I have now downloaded 'ubuntu-6.10-desktop-powerpc.iso'. It fits on a CD and now I can boot from it, thanks for all the help with getting it to work.
If you want Ubuntu for PowerPC, Click here and it's the second one from the top.