I’m not sure if you have a problem simply with the conversion program or if you don’t have any program associated with the .vob file extension. Can you play dvd files ok? In other words, do you have a dvd decoder installed?
I don’t use WinAVI, so I can’t really help with that program. There are many other free conversion programs though, so you could test the conversion in one of them and see if it will produce a dvd. Look at AVStoDVD, DVDFlick or FAVC.