Best backwards compatible way to programmatically capture sound going to speakers

What would be the best approach to take in order to achieve a backwards compatible (Windows XP through Windows 7) way to capture sound that is being sent to the speakers on a machine, even if the audio driver doesn't expose the "Stereo Mix" recording device.

For extra points, it would be great if this approach allowe开发者_C百科d for capturing sound from a single application only (excluding sounds from other apps and Windows itself).

Is writing a loopback audio driver the only solution?

AFAIK there is no realiable way of doing this. Even if a card does have something like a stereo mix its a nightmare under XP and below due to a lack of coherent interfaces. CoreAudio under Vista and 7 massively improves matters but if you don't have stereo mix then you won't get far ...