The mic-in port can also function as a stereo input port, IIRC. That could accept two microphones through a splitter, although mic signals are unamplified and I don't know how feasible it is to do the amplification in software. That is to say, the stereo in signals ARE pre-amplified, and the mic signals normally aren't.
You can also do multi-track recording from multiple mice by using one or more USB soundcards, although there are time drift issues with that.
I know that this isn't really entirely related to the original question, but I'd been thinking about it recently.
I actually recorded a two-mic interview on a notebook in the past by putting one mic into the laptop's onboard mic port and using the mic port on a USB soundcard for the second one. They started perfectly in sync but slowly drifted apart. Not enough to be completely out of sync, but enough to make really annoying echo effects when played back on top of each other. I figure they were maybe a second off after perhaps an hour of recording. I'm sure this could be fixed while recording with the proper software. I was using n-track studio at the time.