For decoding install ffdshow and XviD. I believe ffdshow handles a wider variety of formats, but you can install both without any problems.
ffdshow tryouts project: Discussion & Development thread at Doom9
http://forum.doom9.org/showthread.ph...ht=MP4+decoder
ffdshow tryouts download page
http://sourceforge.net/project/showf...roup_id=173941
ffdshow tryouts direct download link
http://umn.dl.sourceforge.net/source...0322_clsid.exe
XviD forum at Doom9
http://forum.doom9.org/forumdisplay.php?s=&forumid=52
XviD download page
http://www.koepi.org/xvid.shtml
XviD direct download link
http://www.koepi.org/XviD-1.1.2-01112006.exe