If you are trying to play AVI video files, I would download and install the DivX and XviD codecs. For DivX, you only need the codec (not the player or anything else).

http://www.divx.com/
http://www.xvid.org/

Hope this helps

Dano

P.S. I use a free program called AVICodec to determine what codecs video files need. Just drag and drop files. If you don't have the codec on your computer, it has links to the website where you can get it!