You can record any sound made on your computer with Audacity, however the option to do so is disabled by default on Vista/ Windows 7, by Microsoft to prevent copying copy righted material. For those of you who want to record material off dvds/ video see link below
You are looking for stereo mix, and can also access this through
Start Menu> Control Panel> Hardware and Sound> Manage Audio Devices
Once you've done that you simply open up Audacity go to Edit> Preferences and in the Audio I/O tab, there's the drop down menus for "Recording". Select the drop down menu for "Device" and click on Stereo mix.
Now you will be able to record to your hearts content (or according to how large your hard drive space is).
Yeah, it is fun playing around with the sound. I once did a mod that played rock music for Tech, Techno Dance for Vasari, and classical for Advent just for laughs.