I installed Lubuntu 12.10 PPC alt. Install on my ibook g4, yaboot failed to install so I used the advice given in the PPC FAQ, "I've lost yaboot what can I do, and I was able to boot to a black screen with and move the arrow but that's all, when trying to login by pressing ctrl+alt+f1 I kept getting "invalid" login. I reinstalled and yaboot failed again, except this time I am unable to boot even to a black screen and trying to login via pressing ctrl+alt+f1 still gives me an invalid login message despite the fact I know 100% I am correctly typing in my username and password.
EDIT: For some reason, another reinstall went smoothly despite using the disc. I was able to login but had to use single user mode to reset my password as the invalid login error occurred again.