Ok, here's what you do:
1) Go to your friends house, take a FireWire Cable with you.
2) Turn his Mac on, turn yours off.
3) Plug the Firewire Cable into any available Firewire port on his Mac.
4) Plug the Firewire cable into any available Firewire port on your Mac.
5) Turn on your Mac, hold down the T key until you you see the triangle looking Firewire symbol on your screen.
6) Watch his desktop for your Macs Drive icon to mount on his Mac. You have just booted your Mac into "Target Firewire Mode".
7) Open Disc Utility on his Mac and let it repair your hard drive, run both Disc Check and repair permissions.
8) When done, unplug your Mac and reboot.
At worst you will waste an hour, at best you will save $129 on the 10.4 disc and fix your computer.
I did this just a few weeks ago with my G5 and my iBook. This saved me from a reinstall and confirmed that my issues (including Kernal Panics) were not Hardware problems as I had feared.