If you're not shy at the command line, you can use the cat command to do this. I don't know how well it will work, but if it's VOB's that have been ripped, I used to do something similar to this in DOS with no problem.
use the command like this 'cat vob1 vob2 vob3 > reallybigvob' you can even change the file extension to .mpg (which is all a VOB is) and then import it and split it using the program used to create the DVD or something. I don't know how that workflow goes, since I typically just rip and concatenate out to mpg's for storage.