Doogal4 is a lifesaver! I've spent so much time trying to find a solution on the Web, and I've spent so much time downloading software to try to fix the problem...
My experience (and other posts in various forums on the web) indicates that the problem only comes up when trying to convert XVID files with variable bitrate audio to burn on DVD.
From various other forums, I've tried a half-dozen programs to re-encode the file before putting it into
Nero, but (as Doogal4 implies), the problem seems to be with Nero's own XVID codec. Disable the two files, and XVID's XVID codec gets used instead. Of course, you need to have installed the XVID codec from XVID (it's freeware, go to the xvid website and get it).
One clarification -- I didn't have any file named NeAudio2.ax, but I do have a NeAudio.ax. I'm running an older version of Nero, so I'm guessing that NeAudio2.ax is a revision. I renamed NeAudio.ax to "oldNeAudio.ax", NeVideo.ax to "oldNeVideo.ax", and tried re-encoding two discs that had given me serious sync issues. They're now playing beautifully. Thank you for the tip!