Rob, this is what I do---and it works every time---to record DVD's from my timeline in Vegas.
1. I downloaded the free Debugmode frameserver from
http://www.debugmode.com/frameserver. youi'll have to install it in your plugins folder inside Vegas. This way, when you have your project open and all your effects rendered, you can click File-Render as-Debugmode frameserver. This will open some more boxes asking where to install the file and what RGB settings you want. Pick RGB32. When you click okay, the software will install a ghost file on your hard driver wherever you told it. In this manner, you don't have to render your entire timeline into a suitable avi file that has to be encoded into MPEG2 later.
2. Use Tsunami MPEG Encoder (TMPEnc), which can be bought at
http://www.tmpgenc.net, to change the ghost file into an .M2v file, along with a .wav file for your audio. There are alot of great controls on TMPGEnc, such as variable bit rate settings, that will allow you to fit more video on a SL DVD. I do church videos all the time in the CQ (Constant Quality) mode at 6000kb/sec, with dancing and skits and such, and can produce a quality 90 minute video.
Make sure you don't push the limit on your video space you need on your disc, however. You need to leave a little space for menus, if you need them, and button navigation. You can also save some space by rendering your audio separately in Vegas as an .ac3 file. This will take up less space on your DVD than if you used a .wav file.
Not knowing what app you'll be using to burn the DVD's, I am offering generalities at this point. But I hope the info I've given here gets you pointed in the right direction.
