I've recorded sound from websites before with an application called Audio Hijack, but I use a mac. I'm sure there's got to be a similar program for PC, check download.com
Play the song through your speakers, hold a tape recorder up to your speakers and record. Then using a cheap headset microphone connected to your computer, playback the tape into the mic using sndrec32.
Or just use a recording program like Cool Edit to record from the stereo wave mix.