1. Download the K-Lite Mega Codec Pack.
K-Lite Codec-Pack is a collection of codecs and related tools. The K-Lite Codec Pack is designed as a user-friendly solution for playing all your media files.
Features and download can be found here:
http://www.free-codecs.com/download/K_Lite_Mega_Codec_Pack.htm
The Mega-Codecs pack comes with Media Player Classic which once K-lite is installed will play all these files. I know cause thats what I used to watch all these.
2. Think you have all the codec you can handle then try VLC player,
http://www.videolan.org/mirror.php?file=vlc/0.8.6b/win32/vlc-0.8.6b-win32.exe.
