Record Audio Output

DirectSoundCapture will capture from the selected recording device/channel in the Windows volume control utility. You should find a channel called "Wave Out Mix" or "Stereo Mix" or something similar, and check it as the selected recording channel. Note that not all cards can reroute the stereo mix to the recording unit, but many do...

I believe the SDK's DirectSound samples are a good start... (of course, choosing which channel to record from is not something that can be done programmatically by DirectSound).

This sample does exactly what you want:
http://www.codeproject.com/audio/admixer.asp?df=100&forumid=13301&exp=0&select=1505444