Hi,
I can confirm that I was able to boot from the image from a USB key using the line from Ben Westover in the previous message.
A CD-RW and two USB keys failed to work, it worked on the third USB key -- who knows why.
I have some slowness and error messages on boot ("ata1: SRST failed (errno=-16)") which I assume are because my IDE device is a CompactFlash card, but it all works fine after a long pause. I will dig into that issue at another time.
Also, I chose all the defaults and the installation booted fine.
This is a PowerBook G4 Aluminum 12" with a G4, model "PowerBook6,4".
Thanks everyone!
Sam