[saltman]

1. As far as I am aware Vegas only does 2 pass VBR. You can use an external encoder (bypassing Vegas's internal Mainconcept encoder) with Vegas such as one from Canopus that does 6 pass VBR. That's probably what you've seen.
2. You want to go File Properties and make it NTSC WS with LPCM in vegas. Then when you go File Render the options depend on the length of the disc. You're gonna need a bitrate calculator, use google. You need to render the audio and video separately in Vegas. Start with the filtype mpeg-2, DVDArchitect videostream NTSC WS template. Edit it to use your bitrate choice. Assuming it's less than an hour per disc... use a 2 pass VBR of something like 8200 max, 8100 avg, 8000 min. (I know those numbers are close together but it's been my experience this will have better results than say a 8100 CBR). Then render your audio using the same start and stop points (loop region) using the wav template (48k).
3. You render the video and audio separately in Vegas. Then you combine them with your menus, etc. in DVDA, making sure not to rereder them at this step.