Well, if you have a firewire drive you could try installing to that instead. I don't know what's wrong. I'm on a G5 iMac and it works, though after a while none of my audio visual programs worked at all anymore despite having all the codecs etc. And reinstalling a couple of times. You will find your display is off center once you get it installed, but there's a solution to that here:
You could wait a few days and be bold an just go for Fedora 11, looks like that may be last Fedora release for PowerPC as "primary architecture" and it may be using a different video driver, resolving the off center issue
Is your Mac OS at least working now?