First off, DivX is an AVI format. Not MPG.
Second, it could be as simple as a bad quality disc, and it\'s getting read errors/corruptions when it tries to play a standard file. Try copying it to your harddrive.
The only even remotely used codec for MPG that doesn\'t come standard with the new version of Mplayer - you download that... oh, and manually use mplayer2.exe, it is in the same dir as mplayer.exe. It\'s the old interface (faster, more detailed control options) for mediaplayer, but updated with each version, so it uses modern codecs - is Angel Potion (bah, bad grammer, to tired to fix). It\'s not a great codec but some people still use it. Do a google search for the codec and you\'ll find it.