A few months ago, a friend of mine recorded the Salt Lake City episode of "Insomniac with Dave Atell" and encoded it to mpeg2. Unable to play the file in QuickTime, I found myself trudging through various websites looking for a conversion program that would export the mpeg2 file into a viewable format. Apple offers the mpeg2 codec on their website for $20, and I felt this price was a little hefty just to view this one file. After trying out many different programs, and finding that none of them worked, I decided to call it quits. I had already seen the episode on television and I figured that a digital copy of it wasn't all that important.
But for the longest time, I've had the open-source program MPlayer in my Applications folder, but had rarely used it. Then this morning, just out of morbid curiosity, I dropped the .mpeg file into MPlayer. It worked!
I haven't tried this out with other mpeg2 encoded files, but I'm pretty sure they would work. MPlayer is a very easy to use application. Just drop your files into the "Playlist" window and click play!