Here's an overview for you newbie's out there, to understand what files are contained on a DVD.
VIDEO_TS.* Represents the DVD Video Manager. Must be contained on every DVD. It may contain a Menu and most times it contains fbi warnings and Dolby Digital presentations. VTS_xx_x.* Represents a title set. A title set may contain a movie and a menu. It also can contain a menu only without a movie, or the opposite a movie only without a menu.
A DVD must at least contain one title set numbered as 1 (means VTS_01_x.xxx must exist on the DVD).
*.IFO containes control information to navigate through a DVD. *.BUP are backups of the IFO file, if the IFO gets corrupt *0.VOB containes the Menu *n.VOB containes the movie/extra itself (where n=1-9)