I understand you are referring to DVD authoring software...If you are rendering to mpeg2 on Vegas (excellent quality as far as I'm concerned for domestic/home dvds) you should be looking for an authoring software which will not re-render your files. Since I am an amateur at vid editing and basically play with family movies, I have looked around for low cost authoring software. So far have tried Ulead dvd movie factory (you can download fully functional 30 day demo from Ulead's site) and Dazzle DVD complete. Both accept VV rendered mpeg2 files with no re-rendering. They differ somewhat in the features they offer, though IMHO Dazzle DVD complete is slightly more versatile and allows for introductory clip for example, but is slightly more pricey at approx 99$ (vs 49$ of movie factory). Try them both and take your pick.
As far as the more prosumer/full pro authoring softwares, I'm afraid there is not much I can say...

Hope this was useful...