Sadly you cannot use the audio input / output (it's one way only). You'll have to buy an USB adapter, it will also do the trick, but it's a bit more expensive. Here's one:

http://www.amazon.com/Griffin-Technology-iMic-Audio-Device/dp/B000BVV2IC/ref=sr_1_1?s=electronics&ie=UTF8&qid=1328783278&sr=1-1

If I were you I'd use the Headphones just for the audio output and the Built in Macbook mic.

I hope that helped ;)