As usual, your mileage may vary, but this link gave me life the other night:
My Mac mini G4 is a cherished machine. I love the form factor. I love G4 processors. It is superbly limited which makes it not age so well, but nonetheless, it is beloved. After running OS9 on it, despite some sound limitations, I decided to push it in a new direction as a Linux box. Enter MacBuntu-Remix, available over on the MacRumors Forums.
BTW – a review is forthcoming.
But first, the Mac mini G4 is notorious for having an awful CD/DVD drive. This unit’s drive long ago bit the dust. I was using an external FireWire drive, but it too was whining every time I opened it up. It finally would not read a recently burnt disc image.
I fiddled with Target Disk Mode, which is still amazing technology, and gave up only to discover the above technique. Holding down the option key on boot will not generally allow us to boot off of a USB Drive, but using the Open Firmware gimmick above does. A great tip to turn some of those old USB drives into serviceable backup booting options for these old Macs.