If I cut the audio I will then have to re-render the entire project - right?

Not necessarily. DVDA can (and usually prefers to) use separate video and audio files. It shouldn't be an issue to simply re-create the audio as a separate file and then add it to the DVDA project in place of using what's in the MPEG file. Drop the MPEG file onto a Vegas timeline, trim the audio, and render it out to a Dolby AC3 file (or WAV, if you prefer). Go back to DVDA, navigate into the item in question, click the Audio tab, and change the audio reference (Properties window) to indicate your new file.

Assuming your MPEG file is using MPEG audio, this should work (I think) in any version of Vegas or Vegas Movie Studio. If it's using AC3 audio already, you'll need the latest update because the original release of Vegas 6.0 couldn't import AC3 audio, only export it. To the best of my knowledge, Vegas Movie Studio doesn't support AC3 audio at all.

Or, if you're in a hurry and this is the only movie going on the disc, just skip all of the above, navigate into the film in question, and drag the out point (yellow triangle at the top right of the timeline) all the way over to where the video ends. DVDA will put everything on the disc, but the movie will stop playing where you set the out point.

Some of this may be moot, though, if your MPEG isn't DVD compliant already, 'cause then DVDA is going to have to re-encode it anyhow. Go to File -> Optimize DVD and see if you have checkmarks (OK) or exclamation points (not OK).

Rob