Videos don't work on High Definetion Audio

I have Windows Vista and have been trying to play movies and TV shows on Winamp. All of my songs work, so I believe it's a Codec problem. Whenever I play videos (mostly .avi files) the video is fine because I have Divx, but do I need another audio Codec maybe? Because the sound is horrible, there's this scratchy sound over all the words.

Do you think this is an hardware problem..? or do I need a certain Codec, if you have a certain Codec that you would think might work, send it on over.