Sound not working on a DivX clip...

I downloaded a DivX video clip from Kazaa. The video is perfect quality, but there's no sound. Any sound codec I should download?
Some movies use AC3- or other less-common-formats for the sound. There are some tools (search on Google) which will help you determine what codecs you need.
Originally posted by Zziggy00@Oct. 26 2002, 11:34 am

Download the newest DivX codec, it's always nice to have version 3.11 around too.

Why is that? I have 3.11 and 5.0.2 I believe. Can someone tell me why I need both of these? How they differ, etc? I know I need 5.0.2 to play all the latest DivX stuff, but why do I still need 3.11 installed?