Sounds like you have the 500MHz, you should consider upgrading your ram to 640MB, and upgrading your hard drive, the 10 gigabyte hd from the ibooks, is a 4200 RPM, so upgrading to a bigger and fast hard drive wouldn't hurt. What version of OS X are you running? Those shipped with 10.2 jaguar correct?
Try booting out of open firmware.
When you first press the power button, immediately press ( Command alt O F )
it will bring you to a white screen, that will give you bios info ect.
and see if that gets you any further, you can also reset your nvram which may help, consider doing a PRAM reset. In open firmware:
Press enter after each and "ok" will be displayed, after you type reset-all your mac will restart.
To do a PRAM reset press the power button and immediately press command alt P R
MacBook 2.16 Core 2 Duo, 2 gigs of ram, 120 gig hard drive Snow Leopard 10.6
PowerBook G4 15" High Res 1.67PPC, 2 gigs of ram 160 gig hard drive Leopard 10.5.8
HTC MyTouch 3G 4 Gigabytes Unlocked, Rooted 2.0 Eclair