Sure. You export the sound as I have mentioned it above.
Then you use Headac3he or BeSweed to get rid of the AC3 and output a wave file.
If you succeeded, the wave file will be about 900mb. Okay, then open Virtual dub (not mod, cause I don't really know how to do it with VDub mod) and select "Video > Direct stream copy" then "Audio > Wave audio" and select the wave file outputted by Headac3he/BeSweet. When the wave file is loaded, click "Audio > Compression" and select something like mp3 (or whatever you prefer) and the bitrate you'd like to have.
When finished just click "File > Save avi" and save the avi
What's the sense? You'll have normal mp3 audio instead of ac3 audio in your avi file. the picture quality will be 100% the same cause you've previously selected
direct stream copy on video. so just the audio gets reencoded.
hope you get what I mean.