Streaming a movie from Windows (Media Center??) to A500
I use TVersity to stream to my Android device, Logitech Revue, Original Xbox, Xbox 360, etc. TVersity can transcode the video on the fly. 

I have, in the past, been able to get Matroska container files to play, but not always and with varying results. Sometime they don't play at all, sometime they played fine, and sometimes they play, but the video is choppy and out of sync with the audio. 

Being able to stream the video to your android device will depend on the video codec used to encode the video. If the device does not support the codec, it will not play. AFAIK, android, out of the box, does not support the matroska container, actually, there are a lot of formats that android does not support. Using something like TVersity on your "Media Server" allows you to transcode these videos in a format that the device will understand, and can play.