Q: Trying to install Leopard with broken Combo Drive

Hi,
I recently got a Powerbook G4 Titanium 1 GB with a broken combo drive. It has OS X 10.2 on it an I would like to wipe and install Leopard. I have tried booting off an external USB drive but it won't show up in the boot manager (option during startup). So I put a small 20GB drive in my powermac G4 and made an image of the install disc and restored to the drive, removed the main drive, and booted the powermac into firewire target mode, hooked it to the powerbook, and told the powerbook to boot from it. The powerbook stayed on the grey apple loading screen overnight so I have come here to see any suggestions without buying an external firewire dvd drive.