The correct windows solution is Total Recorder. It inserts itself as a shim in the audio driver allowing you to stream all wave audio to disk. I believe this is the functional equivalent of the macintosh program mentioned above.

Another way is to save the stream and transcode. There are programs that will save RealAudio streams to disk (I use NetTransport) and others which will transcode RealAudio files into MP3 (I use Streambox Ripper).