My method is to:
#1 - Finish my editing within V7
#2 - Render a completed/finished AVI. I do this to ensure I have at least a BIG ViD finished!
#3 - I then render from this finished AVI an MPG2 Video Stream only:
MyProject.mpg
#4 - I then I then render from this finished AVI an AC3 audio only:
MyProject.ac3
#5 - Open DVDA4
#6 - Locate my newly rendered mpg drag directly onto the MAIN Menu. This appears in the timeline for the video
#7 - Locate my newly rendered AC3 file and drop it UNDER the MPG timeline.
#8 - Preview to check
#9 - Go > Prepare and I take note of any warnings that need my attention and proceed to finish prepare.
#10 - Once I've finished Preparing I then burn
So, to recap: Edit and Render in Vegas > Prepare and Burn within DVDA4
Hope this helps,
Grazie