Hi, Found this tidbit of info: You need to install FFDShow. It comes with various audio/video filters. MPC will use all available filters to render the files. Thus by installing ffdshow MPC will call the required filter for rendering the file. I too was searching and have only seen the above mentioned codec as a plugin. If I run across anymore I will simply edit this post and add to it. By the way FFDShow can be found in the software tab at the top of the page http://www.afterdawn.com/software/video_software/codecs_and_filters/ffdshow.cfm. Will request to be moved to software discussion as this has nothing to do with divx/ xvid per your question.
MPC uses directshow*, so it can use any directshow filter (ffdshow included). In some cases this means disabling built in filters. *Also has shockwave, quicktime and real media modes for those formats. But that can be toggled under formats in the options.
