Well, you can record in stereo from the Line In, if you have a stereo signal going into the line in, that is. For example, you can record stereo effects on a guitar. Just set the multitrack that you're recording on to "stereo" instead of LEFT or RIGHT.
But if you're talking about actual mics, yeah...you need more than one input on your soundcard, or an external mixer....
....or a preamp with 2 outputs (like a DMP3)...I do that...then run both of the outputs to an adapter that narrows down into a 1/8" input to the soundcard. Set one of the tracks to record LEFT and another one to record RIGHT if you want to have control over each of them.