New MacBook, External Mic Problems.

Hi, I recently bought a new MacBook and I bought and external microphone, which connects into the port on the side.

The only thing is when I connect it, my MacBook doesn't recognize it.

E.g In iChat when I try to change the audio source to line in and speak no one can hear me.

And in GarageBand when I change the audio source my voice does not record?

Am I being plain dumb and missing something?

Thanks

are you missing a driver for the mic?