Most camcorders have a set of RCA plugs for output. The Yellow plug is video, the other is audio (if you have two others, a red and a white, then you have a stereo camcorder, either line will do). Grab an RCA cord and plug it into your camera. Grab (one of the) audio connections on the other end, and adapt it by plugging an RCA to Miniature speaker headphone jacks (RCA female on one end, regular mini speaker headphone male plug on the other); and plug that into the cable, and the other end into the LINE-IN plug of your PC.
Then, use Windows "Sound Recorder" to record the sound as a WAV file while playing back on your camcorder. You may need to play with audio settings, making sure LINE-IN is enabled (not muted) and Sound Recorder is recording from that channel, etc.
Lastly use a WAV to MP3 conversion program (search the net) to cut the size of the WAV file down (if needed...wave files can be about 10MB per minute and MP3 files are about 1/10th that size).
That's the broad brush strokes of how I would do it.
TJR
