DVDA will marry your audio to your video if its in the same directory as the video and has exactly the same root name, for example xxyDr.mpg and xxyDr.ac3 . Otherwise, you can manually drop it in.
The next question is why you are having a problem getting (presumaby) 1.5 hrs of video on the disc.
Also, be sure you are not rendering your mpeg from the mpeg you made on the first try. Go back to the original project.
Gary Kleiner
Learn Vegas and DVD Architect
http://www.VegasTrainingAndTools.com