I tried to google/forum as much as possible, couldn't find a fix.

I am unable to boot from any PPC iso, from 10.10 to 12.04. I burned the image on two different computers, slow speeds, checked md5, etc etc. In all scenarios, holding 'c' at boot eventually boots into 10.5.8, and 'alt' at boot does indeed show a linuxCD, but selecting it circles back into the startup disk chooser (albeit in awful 8-bit graphics).

As we cannot boot from USB, does anybody know how I can boot/install Ubuntu on my PowerBook G4 15"?

Thanks!