I recorded the sound through the pickup in my guitar to my PC. The pickup is a K&K Trinity system - very nice.
I then converted the recording to a WAV file. I then imported the video to a PC using a video capture card.
Then I used Windows Movie Maker to synch the sound to the video - which was not a problem free experience!!
Some people can get really good recordings straight through the camcorder, but it can also sound a bit rough.