Some movies are created with WMA sound format which is unrecognizable by the mp3 codecs of DivX versions higher than 3. In such cases your player starts searching the net for the appropriate codec and never finds it because there is no such available for download.
The only available appropriate DivX audio codec comes with the DivX 3.11 alpha codec installation pack (other repacks also) - DivXa32.acm. So now you've got an unique DivX 3.11 Alpha repack that will install only the missing audio decompressor, will add an item in your audio compression manager (for win 9x - control panel / multimedia / devices / audio compression codecs) and also an option for uninstallation from control panel (add/remove programs).
This is an advantage over installing the whole of the DivX 3.11 pack because it installs its older video codecs which you do not need and it overwrites the registry and uninstall information which makes it impossible to uninstall DivX 3.11 Alpha and the other later DivX codec version you might have separately. This may cause some undesired behaviour of your codecs and players. All you need to do for hearing the WMA sound of your movie is to install this pack.