Hey Spizz,
Try loading the AVI in VDub and start at the first frame and step one frame at a time for a dozen or so frames. Is there a frame near the beginning that says something like "B Frame Decoder Lag"? That would certainly screw up the sync. Even if you don't see that, how about trying this: Load it, and have VDub jump to the first (or next) keyframe. Hit mark in, go to the end of the file, and hit mark out. Save it, and try that in DivXtoDVD.
If that doesn't work, you'll have to demux, reset the audio delay in an audio editor, then reauthor the DVD. It CAN be done with freeware: PgcDeMux to demultiplex, BeSweet using the frontend BeSweet GUI v.0.7b4 for the audio, and Rejig to do basic (no menu) authoring. It'll take some patience on your part, is this file worth the effort?
Good luck.
