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 here, https://wiki.ubuntu.com/PowerPCFAQ#I.27ve_lost_yaboot.2C_what_can_I_do.3F and I was able to boot to a black screen with and move the arrow but thats all, when trying to login by pressting 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.