No, you can't just take two vobs on a DVD and expect that it is a compliant DVD. You will have to author the DVD. Two possibilities:
1. use an authoring program that can import VOBs (e.g. DVDlab or TMPGEnc DVD Author)
2. extract the MPEG streams from the VOBs (e.g. Ulead DVDMovieFactory can do that) and create a DVD with any authoring program.