Jack,
The fact that you have VOB files on the DVD implies that the ‘raw’ footage has been processed by some DVD authoring s/w.
To be able to edit, you must first rip the DVD to at least get an AVI wrapper around the material. Then, when it’s brought into the Vegas timeline, you should be able to handle it just like any AVI clip.
I did this for some promotional material where a customer’s commercials were supplied to me as a DVD (it would play in my settop box).
I used Nero Recode and also DVDDecrypt to rip the material. I think I also needed to used TMPGEnc Xpress at some point to re-encode, but I forget. Some of the ripped files would just not play nice with some s/w combos.
HTH,
Tom