DVD authoring in Vegas requires an MPEG-2 file for your video and an AC-3 file for your audio.
I hope that you have DVD Architect as these steps assume that you do.
Give both files the same name and render them (video and audio) to the same folder.
Render your video to MPEG-2 using the following steps.
If your video is not in widescreen mode, then use the “DVD Architect NTSC DV video stream” template, otherwise do as indicated.

Once you have this template selected, click the Custom button and modify as show below (a custom CBR bitrate of 8,000,000). This is done to maximize quality in the finished product. This template can be saved for future use if desired.

Once your video is rendered, it’s time to do your audio as shown below.

Once this is done, create a new folder on your hard drive for the DVD files.
Now load up DVD Architect, go File – New – Single Movie. If it’s in widescreen mode, change the video format mode to reflect that.

Follow the prompts to go to the folder where your newly rendered files are. Click on the video file and, as long as the audio has the same name, it will be automatically loaded.
Once this is done, you;ll be returned to the main screen.
Click Make DVD on this screen and then Prepare.
Click on the folder that you created earlier and your DVD files (inside of AUDIO_TS and VIDEO_TS folders) will be created in that folder.
Give this folder to your friend for burning purposes.
I hope that wasn’t too confusing 🙂