Use rtmpsrv or rtmpsuck to find out what parameters are needed for rtmpdump.

You can also many other RTMP Flash stream recorders here. For example, you can try to download RTMP streams with freeware CooJah + Blader, Orbit Downloader, StreamTransport or shareware Replay Media Catcher, WM Recorder.

And you can capture RTMP streams with freeware CooJah, Orbit Grab Pro or shareware Replay Media Catcher.