Real Instrument on Garageband [MacBook Pro]

Hi all,

Okay, first the specs:
Macbook Pro aluminum running 10.5.8. This is the model that comes with a 'combo jack' which includes input/output.
I bought a monster cable:Amazon.com: Istudiolink Instrument Cable: Electronics to connect my guitar to the computer.
I went to System Preferences > Sound and connected the cable, apparently, the macbook thinks it is a headphone, and not a microphone. That being said, I am not able to record music played from the guitar on garageband.
What can I do? Do I need something else?

Thanks,
Rafael

Hmm. How does the computer know which it is? Wouldn't the "combo jack" be a nuisance.

Nevermind, I figured it out. I had to go to System Preferences > Sound and change "use audio port for: sound input". Kind of obvious, but I had missed it.


Rafael