Last week I had a problem. A customer had an iMac G4 that wouldn't boot. He was told it was a hardware problem by another shop. It looked like a software issue to me. Without reloading how do you tell?
I thought... I wish Knoppix supported PowerPC. So I started searching and came across Unbuntu Linux http://www.ubuntulinux.org/
Live CD worked perfect. I was able to boot the machine and verify that everything worked. Now to reload OSX... but that's another story.