when you author a dvd what generally happens is that you'll feed the authoring program a mpeg2 file and a audio file wav or something compressed. what i usually do is, after doing all my editing on a video editor, export the video audio to a wav file. then using something like cool edit or soundforge sync the rough and the new audio together. from there you get the new audio sync'd up with the video.
of course in russ's case, he could probably also sync up the audio in the video editor. eric will have to also find a program to convert the dvd back to either one big avi or split back to mpeg2/audio files.
this is probably difficult to understand. i'm sure theres easier to understand tutorials out there somewhere.