Sadly, I wasn't able to get this to work under Vista.
I see four methods so far:
1) Set up an analog loopback via line-in. That sucks though, as it means that the signal goes through DA and AD phases.
2) Set up a digital synchronous loopback via SPDIF. I can't do that though, as I lack the SPDIF input jack, and it's also not quite optimal.
3) Search for a loopback virtual input device driver for Vista.
4) Buy a soundcard with internal routing. But buying a soundcard for this purpose is too extreme.
That's all the ideas I've got at the moment. I don't understand why that isn't there from the outset, if that's a correct assumption. It's so incredibly useful to have. The DRM system will surely be able to safeguard protected content.
Maybe one could have an ASIO driver and force the output of the programs into it somehow, and then reroute the output of the driver to disk.
If it is possible, then please, someone enlighten me!
The funny thing is that I first tried to record it, and I didn't understand the volume was so low, until I noticed some strange background noise, and sure enough, it was my stashed-away microphone that had been recording.