Well unlike no-overhead video capture (which requires a capture card), you can do no-overhead audio capture for cheap. Grab a stereo-stereo audio cable, direct your line out to another computer's line in -> voila. Then just mux it in to the video later.
If you happen to have a full duplex sound card or two sound cards (perhaps one of them being a USB or firewire card) you might even be able to use this technique on the same computer with much less overhead than capturing the sound directly. I used to capture audio this way sometimes with a full duplex card or a USB sound card (quite a while ago). I can't be sure about the overhead, though, without testing it.
Originally Posted by curaga