Audio Codecs help

Hey I was wondering where I could find some help and troubleshooting on audio codecs. I have some different video files on my computer that works except there is no sound (I play them in Windows Media player). These files are usually either .avi or Divx. I was just wondering where I could go to possibly find a missing Audio codec that I don't have so that I could get sound when watching these video files.

Thanks a lot everyone.

FYI (These video files are supposed to have audio in them).

I sure need some help! Is there a place to get new Audio codecs at?

hum... maybe you need to split the audio stream, and reprocess them. try VirtualDub.
Or.. is it possible that you need LAME or other MP3 codec?
splitting them is the first thing in my mind.

Thanks, I'll have to look into it. If anyone has any more info that would be great. I'll have to give Virtual Dub a try when I have more free time and see if I can fix it that way. How would I get those other codecs?