How do I read system audio output in windows xp and windows 7?

I'm writing a windows application that lets people do something akin to screencasting. One of the things my applic开发者_如何学Cation needs to allow is to capture the audio being produced by the other applications on the computer to add them to the recording. Some googling indicates that the new WASAPI actually supports doing stuff like this, but is only available on windows vista and windows 7, and a large portion of my target market runs windows xp.

How do I capture audio on windows xp?

Is there some library I can use that wraps the windows sound apis that will make it simpler to do so?

Do I need to install a driver?

It looks like the only solution here that works on windows xp is to write an audio driver that makes the audio that's sent to it available to userland. Fortunately someone's already done this ( http://software.muzychenko.net/eng/vac.htm ). Unfortunately he charges money.