Mplayer & Xvid is great until someone wraps things up in a .mkv wrapper! It took me a few days to: a)figure out which codec was missing and then b) figure out how to find said codec so I could play (deleted: currently-in-theatres-movie-name-here)! I think I have every codec known to man on my machine after trying to fix this. The secret to my movie was installing the Realplayer's most recent release (if you hunt you can find the corporate/less-intrusive version). The codec I needed was not part of any codec bundle known to man.

-Zeke