I dont think so but you may be able to just change the container of the file to allow it to play to something like AVi or Mpeg4.
http://yamb.unite-video.com/ is a good free program that can change the container of a file to Mpeg-4. Only other way is to re-encode the whole file and that would take alot longer depending on the file size.
Note* if you have to re-encode it here is a guide -
http://www.afterdawn.com/guides/arch...r_xbox_360.cfm There may be eaiser ways of doing it and better software but thats just a qiuck guide I found for you.
Note2* I think there are programs that can stream MKV files to your 360 to but I have not really looked into this maybe someone here knows more and can assit you in that way.