Only the USB 1.1 iMac DV/PM G4 (Sawtooth on) and Pismo + G3 iBooks+ some G4 powerbooks were bootable. Once USB 2.0 came out, apple nixed the ability until the intel machines came out. Not even the PowerMac G5 could do it. Kind of frustrating, as all they left was the FireWire port, and I had a machine at one time that the firewire chipset went out on it. (iBook G4) with no way to boot from it when the HDD went bad. DVD/CD-RW also was not reading correctly.

So I had no option but to swap a new motherboard in it to get anything to work since it turned out that part of the chipset went south, and the IDE didn't work