I was having the same problem myself for the longest time. I would try to look at some new, errr... "stuff" I downloaded and there would be no audio. Would really piss me off. Anyway, the codec I eventually tracked it down to (and the one you're probably looking for) is DiVX ;-) Audio. For the uninformed and curious, it's a hacked and lousy version of Windows Media Audio. Nimo has it, so you can just download that and be all set. A word of warning, though: the last time I checked, the installer for version 5 was corrupted, so you may want to look for version 4.4 instead.