Problem installing Leopard with external HD

So I racked my brain trying to figure out why my PPC Powerbook G4 with 10.3.9 won't boot my external HD from startup. I'm trying to install Leopard, I got the .dmg and restored the install DVD image onto my partitioned external HD and everything went perfect except for the last step! I went into startup utility and I was able to see the external HD with Leopard but once I clicked on "restart" all I get is that error noise (the one that sounds like an empty drum or something). I've started to narrow down what it might be, I think I can Rule out the possibility that it's the HD because I also had a MacBook at the moment with tiger and it was able to restart on that same HD with no Problem. The HD I'm Using is a Seagate 80GB with USB2.0. I Think I read somewhere that PowerBooks can't boot from USB only FireWire but I'm not Sure. I even tried to restart my Mac holding down option so I can get to the screen where I can choose my HD to boot from but it doesn't even show up there. Does anybody out there no what will boot from startup for me or how I can fix this problem?!?!? By the way I also tried to install Leopard via iPod and that wouldn't work either, it wouldn't finish burning the image. Anyway here are the specs on my PowereBook G4

Machine Model: PowerBook G4 15"
CPU Type: PowerPC G4 (1.1)
Number Of CPUs: 1
CPU Speed: 1.33 GHz
L2 Cache (per CPU): 512 KB
Memory: 512 MB
Bus Speed: 167 MHz
Boot ROM Version: 4.8.6f0

You will need get the install media of OS X 10.5. Some that you can boot from it.