My suggestion.
1. Produce your project as a Mpeg 2 DVD HQ file
1-1 Check it has the audio
2. Bring the mpeg back into PD as a new project
3. Add your chapters
4. Create your finished DVD
Test PD - try this as well
1. Open PD - new project
2. Drag into the time-line two or three Aquarium.mpg
3. Add an audio file to a time-line
4. Put another audio file into the other autio time-line
5. Create a DVD (to your Hard Drive) - put it into the My Works Directory
6. Play the Vob files in this DVD with you Video player software
Repeat this test but this time change 6... and add a voice over.
You mentioned in our phone conversation you have Vista. Please contact Tech Support and state the actions you have carried out and ask specifically if there are issues with Vista that would/could cause this problem.
Dafydd