Best way i found to see exactly what codec you need is to use DivX player. If you try to play somethign you are missing a codec for just right click on the file in the play list and hit error details or something like that. You will get a little prompt saying 'missing xxxxxx codec' or something along those lines. just google what it says you dont have and get it. also i noticed that after i installed the codec pack that comes with divx i have had almost no missing codec files. divx is a free, and pay version if you want. dvd/media player. I just used it for its codecs and stick to winamp for my player.