How to choose input/output on mic/headphone

Hi

Is there a mic port on the new Air?

I want to digitize some cassettes and was going to use Audacity. I"m using stereo plugs connecting to a deck.

But Audacity is only picking up the internal mic. Despite my worries it's all Audacity's fault, I see in the Sys Prefs that the only option for input is the internal mic. Maybe it needs to recognize the port, tho I don't see how.

If there is NO port, and it's only a headphones port, how do I connect a stereo plug to the Air? Thru usb?

best,

karen