How to upgrade OS on Mac Mini with external USB Drive?

We have a G4 Mac Mini, circa 2005, running Mac OS X 10.4 Tiger, and we want to upgrade to 10.5 Leopard. We have a Leopard install disk, but the optical drive in this mini is broken. So we transferred the install disk image to a USB HDD, but now we can't figure out how to boot off it.

From what I've read in Mac forums, some PPC Macs, including some G4's, have been able to boot from USB, even though it sounds like this wasn't officially supported, and it may well depend on the specific model of USB drive and Mac. My Mac says CPU is "PowerPC G4 (1.2)" and Boot ROM is "4.8.9f4". I was hoping I might just find somebody here who had that same Mac Mini and find out if they could make it work. I'd especially like to know any specifics about the USB drive they found success with. Any insights at all would be appreciated. Thanks.

Solution 1:

On a PPC Mac such as your G4 Mac Mini, you have to use a Firewire drive. USB booting wasn't really supported before the Intel Macs. You can use a Firewire optical external drive, a Firewire harddrive that has the OS Installer restored to it, put the Mac mini into Target Disk mode and install OS X on a Mac with a working optical drive, or you could even use NetInstall on a MacOS X Server machine.