Not sure if it's the quickest way but the easiest thing I can think of is to download Audacity and then set the recorder to "stereo mix"....Granted, this will record any sound that your pc is producing (ie mouse clicks, new mail alerts, etc) so make sure you turn that stuff off while you're recording. Then you can export as mp3 or wav and be the cool kid on the block with your new sounds
Hope that helps!