why is my mac not booting xubuntu and says: this disk was not repairable by this comuter (usb)

Why is my ibook g4 not booting from Xubuntu for ppc (power pc) it always says :this disk was not repairable (REPAIRABLE) by this computer... And when i go into boot selection on boot (ALT key) i click on usb it has little charictor for linux - and then my screen flashes and goes back to boot selection and the letters are all blurry: for exe: HD is blurry). please answer fast!