If you want the highest quality audio, render a separate PCM (.wav) audio file in Vegas, marry that with the MPEG in DVDA, and choose PCM as the compression option in DVDA.

Thanks SonicEPM,
So in V4, render the Mpeg2 as usual (default) but also render a .wav; then double-click both in DVDA to add to menu and then select optimize (from the "Make DVD" dialogue)then PCM in the drop-down under media audio settings?
Thanks again,
Randy

Render an MPEG-2 using one of the DVD Architect render templaes, and render again as 48k PCM wav, same name, same folder as the mpeg. Load those in DVDA, choose PCM in the optimize dialog and the files should be able to be prepared for burning without recompression. Check the DVD Arch help file for no-recompress format settings.

Sorry but I'm back.
Okay, to keep this breif: Yesterday, I rendered a .wav of the project and tried to select it in the media properties/audio dialogue (to the right of the timeline) but I get the error "Selected file is not of the required type". I spent quite a bit of time on the menu selection and hope I don't have to do it again but I wonder if I need to render the mpeg2 again as video only to work with the .wav I created.
Thanks,
Randy

All is well, thank you very much SonicEPM.
Randy

All was well until I started to actually prepare and burn. The dialogue I spoke of accepted the video only and the .wav so I went to optimize and selected PCM on everything and it still says it's going to recompress! What am I missing here?
Thanks,
Randy

So I started from scratch, added my markers for chapters in V4, added the 48k, 24 bit .wav and video only mpeg2. Everything looked great until I started to render when I get "Warning an error occured while writing a file. The reason for the error could not be determined. FWIW, both files play fine in Windows Media Player.

Make a 16 bit wav not a 24 bit wav.

Basically, as "SonicEPM" said you need to render as follows:
1. render a DVD mpeg2 "VIDEO ONLY" format to produce a video file that does not have an included audio track encoded in the video file. It produces a video only file. As stated previously, Vegas' "DVD Architect" templates produce this kind of output.
2. render a second time, but this time creating an audio only output in the wave format, 16 or 24 bit, 48k mono or stereo (whichever is appropriate). This produces a second separate audio only track. The name of it should be the same name as the file in step '1', but with a 'wav' extension.
3. In DVDA, add the video track where you want it and DVDA will automagically "marry" the separate audio file with it. If not, then simply click on the video thumbnail and choose the audio track you created in step 2.