Welcome to the forums Eyeopr8r.
First of all, when using a dvd made with a dvd-recorder you will need to close (also known as finalize) the dvd in that machine before you can edit it on a computer.
You may have some misunderstanding about the structure of dvd-video however. Individual titles within a dvd, or chapters can span more than one vob file. DVD video is arbitrarily broken into 1gb segments in order to meet the playback requirements of stand alone hardware players. The vob files are contiguous, and the 1gb sections are artificial in other words.
It is possible that one entire operation would be contained in one vob file, but if there is more than one case included on the dvd, you won't be able to select cases by the vob file divisions.
If you have organized the dvd into chapters, and you have each case in a separate chapter it is possible to use DVDDecrypter in IFO mode to select which chapter to remove from the dvd.
If you haven't done that, then you could use DVDShrink in ReAuthor mode and manually select the start and end points that you want to save using the Set Start/End Frames tool. The output would be a small dvd-video with only the section you want removed. Make certain to use No Compression when doing this procedure.
DVDShrink is not a frame accurate tool, but you should be able to get close enough with your cuts for most purposes. If not, you can use a commercial program like VideoReDo, which is frame accurate. I would suggest using VideoReDo TV Suite, since it can make a complete dvd-video from the area cut out.