Movie playback question.

I just loaded a movie into the DivX Player (an .avi movie) and the following window appeared:

The video file you are opening includes audio data that is not recognized by the DivX Player. The file contains the following type of data: Audio data: Tag 8192. You may need to install a new audio codec on your computer to listen to the audio. You can either stop playback now or watch the video without the audio.

What do I do now? Which codec do I need? Where do I get it?

Update: gava pulled the right answer right out of his magic hat :)