One of the best methods I've found is using BlazeAudio, and selecting "Stereo Mix" as the input source. You can record any sound that comes on your computer, I think. I'm not sure, though. It worked while played MIDIs and turned them into mp3s, so it might work for this too. You can always try. Remember, with that trial version you can only start the program 10 times, but you can record to your little heart's content with each time you open it.