ASF Recorder is an open souce Windows Media recorder. It supports mms and http ASF streams only.

You can try VLC Player and MPlayer. Both are open source players that can dump streams. The only problem is that they were not very good at playing/recording RTSP Windows Media streams.

Unfortunately I don't know any other Open Source Windows Media recorders I can suggest.

p.s.
You can try to use mms:// or http:// instead of rtsp://