Windows Media Player is the main program that uses this format and it was developed by Microsoft.
There are some players out there and all I can suggest is try some of the free download sites like www.tudogs.com, www.download.com, etc. Some of the players actually need specific codecs to be downloaded also to support this format. There are converters for video as well, if you need to convert the format to something more widely supported (same download sites).
There is a player that seems quite good at http://mplayerhq.hu/homepage/design7/dload.html
I think Quicktime can play it but needs an addon, which has an associated cost.
Hope this helps.