I have heard many places that PowerPC Macs cannot boot from USB, without advanced coding in Open Firmware.

I have proven this false. I have an iMac G4 with USB 1.1 ports.

I ripped my Mac OS X Tiger DVD, and copied it to a 8GB USB 2.0 drive, plugged it into the iMac.

Without even going into Open Firmware, I held down Option while booting, and guess what.

"Mac OS X Install DVD" showed up. Except the icon wasn't a DVD, it was a hard disk.

I proceeded to boot it.

It booted normally. It even runs faster than the DVD, which is surprising (to me), as it's only USB 1.1.

I'm installing it as I type this, and it's going pretty well.

EDIT: It installed successfully. But, I replaced it with Leopard using the same method, and a processor clock frequency hack using Open Firmware.