I wrote an answer to a person with an audio problem today so I’ll just cut and paste this from that and hope it helps.
“The usual or recommended way to do a DVD out of Vegas is render two separate files – one is mpg2 (and the DEFAULT setting in Vegas is without audio – have to check a box to get audio with it) and the second file is AC3 which is matching audio (render the same area). Both files should have the same name and when you go into DVDA and give it the video file name it will pick up the audio automatically. Then DVDA processes that. DVDA can “prepare and burn” or just “prepare” and most of the experts recommend just use the “prepare” in DVDA, creating the files to disc and then burning with Nero or some other burner program. It is also recommended that you encode in Vegas – NEVER DVDA – because the render engine in Vegas is much better.”
If you follow those steps you should have no problems. If you do have a problem, give more details on how you processed, the burn programs used and steps taken.
JerryW