Guess whut? That's easy. I don't have Vista ofr 7, but I know XP well. I'm not even ON a damned XP machine, and I'm writing this from scratch.
Click on Start.
Click Control Panel.
Choose to switch to Classic View.
Open "Sounds and Audio Devices".
Click the Audio tab.
Click "Volume..." under Sound recording.
Click on Options.
Click Properties.
Enable "Stereo Mix".
Hit OK.
Close the window.
Hit OK.
Exit the Control Panel.
What this does is it will take whatever sound currently is coming out of the speakers, and also send it to the microphone input. For example, say you're running iTunes and Ventrilo, and have done what I stated above. You also have a PTT button bound for Ventrilo. You begin playing "Ain't No Rest For The Wicked" by Cage the Elephant. Now, you hold down your PTT button. Now, anybody in the Ventrilo channel hears what you hear coming out of your speakers, on top of whatever you say into your microphone, so they hear Ain't No Rest For The Wicked as well. To disable this once you're done recording your footage, simply do all the steps again, but disable Stereo Mix.