Tim:
VTS_01_0.VOB an intro or video menu for playing this video clip VTS_01.1.VOB part 1 of the main feature VTS_01.2.VOB part 2 of the main feature VTS_01.3.VOB part 3 of the main feature, etc.
Go Canes:
I have seen many DVDs where Title Set 1 was *not* the main feature; I don't think Title Set 1 = main feature is a safe assumption. If the DVD is a movie, you can look for the largest Title Set. But generally, you have to look at each Title Set to see what they are and determine which Title Set corresponds to which "title" on the DVD.
I haven't seen any where it wasn't, but fair enough. Check you have the right ones.
VTS_01 is supposed to be the *main& title. Some of the early DVD players even had a button to go straight to the main title, and that's how they did it.
I had a home DVD recorder which worked very oddly. For every new recording, it just tacked onto the end of the previous one, it didn't start a new title set (like it ought to).