That is a RealMedia file, playable by the RealPlayer or maybe even VLC Player.
You can use
HandBrake to transcode the .rmvb file to a format iTunes accepts. Use one of the presets, Universal should be fine.
I just tested your file, and VLC Player can play it. Transcoding via Handbrake takes around ten minutes on my 2007 iMac with 2 GHz.