Skip them both and get the pro version of Vegas 6 for only $99 at www.bhphotovideo.com. Unlimited video and audio tracks, excellent color correction tools. If you have a version of VMS or DVDAS that has an AC3 encoder it will automatically appear in Vegas 6. I also picked up a copy of DVDA 3 on eBay for $20 for the subtitle support (not available in VMS7+DVD).
If you have VMS 6, don't get 7, just go with Full 6 from B&H. The only "problem" could be is if you don't have VMS, then you may not have DVD software, as the B&H special doesn't come with DVDA.
Check out Sony's comparison page between VMS6, VMS7 and Vegas 7. They no longer list Vegas 6, but most of the important features ( *except* AC3 encoding) of Vegas 7 are in Vegas 6.
And if you go with the B&H Photo deal you DO need to get a separate DVD authoring app somewhere. You could even go with a version of DVD Architect Studio if you don't need subtitles, multiple audio tracks, angles, etc.