I also have this problem with videowave 8. All of my video files play normally in other programs, but there is an audio-video sync problem when I play or convert with VW8.
I don't have a solution to fix VW8, but I have a workaround. It involves extracting the audio from the mpeg file to a wav file using a 3rd party program. I use goldwave to extract the audio, but I'm sure that there are other programs out there. It's easy in goldwave. Once goldwave is open, hit "file" - "open", then select the file. It should recognize all popular video files since they also contain audio tracks. After it's deflashed and displayed the tracks on a graph, hit "file" - "save as", and save as a wav file. It should take 5 minutes for a 90 minute movie on a fairly robust computer.
Once in VW8, add the video as usual and use the timeline view at the bottom. Right click the video bar to bring up a pop-up menu, hover over edit, and select "native audio...". In the audio editor, slide the "overall volume" bar all the way to the left to effectively mute the audio, then hit OK. Now that the audio is muted, you can add in the uncompressed audio that you extracted earlier to a wav file. Click the video track to highlight it, then click "add background audio" in the "add content" window. A dialogue box will appear and ask where to add the audio. Select "add to sound effect track" it it should be embedded in the video track, not below the video track into the music track. If it adds to the music track below, then you made a different selection in the box. It may still be okay, but if you edit or clip the video, it may not stay in sync.
It's important to extract the audio as a wav file. It's been mentioned before that compressed files like mpeg can sometimes have sync issues in certain players/programs. Since a wav file is uncompressed, you don't run into this problem. It took some trial & error, but now I can convert mpegs to divx using WV8 without any sync problems.
I know that it's a bit combersome, but it works - Hope this helps
JayNOLA