the only way to put a 10.4 onto a firewire disk usually is to clone the install DVD onto the HD and then boot and run the installer from there.
I'm admittedly confused about the above. What is that meant to achieve apart from skip the optical drive?
Here, just for you, I grabbed my 17" PBG4 just to show you how Apple makes it easy to do.
I attached a FW drive and booted up from a retail Leopard DVD. Once in, I used Disk Utility to partition the drive with APM
After that finished I just continued with installation and the Installer saw the FW drive as bootable medium and therefore suitable for installation
And that is all there is to it. No hacks, no jiggery-pokery. FW is just as supported as the IDE bus for booting OSX volumes on a PPC Mac. Except for the B/W PowerMac G3. That Mac was a mess.