iBook won't boot.

The hard drive on my G4 iBook was dying so I replaced it and installed OS 10.5 using target disk mode from my iMac. After partitioning the replacement drive with a "GUID Partition" the install went smoothly. After the install, I shut down and disconnected the firewire cable from the iBook and booted up to a flashing folder icon. If I use target disk mode I can boot off the iBook from my iMac but the iBook won't boot itself. How can I fix this?

You need to use APM not GUID, for PPC Macs. GUID is for Intel Macs.

So if I reformat using APM then reinstall, the iBook will boot to the OS like normal?

Yep. You shouldn't have any problems afterwards.