BeSweet will convert your MPA to AC3 audio. It is a command-line tool so I recommend picking up the BeSweet GUI to accompany it. You can download both at www.doom9.org. That being said, I can't imainge why WinDVD would not play the audio. The player should be displaying "MPEG" for the audio when it's playing. Since there are standalone players that do not support MPEG audio though, I always recommend using Dolby Digital AC3 format anyway. You can't go wrong.