iBook GarageBand and a Guitar Cable

I have a 12" iBook G4 1.2Ghz model and wanted to run my guitar in for some stuff in GarageBand. I bought the Griffin Guitar Cable and plugged it into my headphone jack and got no signal. I am under the impression now that the headphone jack does not double as a mic jack. If I am correct in this what are my options to have a line in for recording?

You need something like Griffin's iMic

http://www.griffintechnology.com/products/imic/

The headphone is an output only plug...You need a USB or firewire port like the one trpnmonkey41 recomended you is your best bet. Some of them even come with MIDI in and out and PHANTOM power for condenser Mic's...Great deal for small projects!.

You will find that that has horrible quality. If you want a nice clean sound then it will have distortion added because of the cheap connection. If you have a guitar amp, then it's better. Guitar > Amp > (from line out on the amp) > iMic > iBook.