If you have CS4 4.1 you can 'edit' VOB's, as long as these adhere to DVD standards and do not contain multi-angle or other non-standard enhancements like DTS. Otherwise use Google to search for a DVD ripper, but be prepared to demux the files and then convert the audio streams to PCM/WAV 48 KHz 16 bit stereo to edit and realize that the final result with not be as pristine as your source, which was already heavily compressed and will now be compressed again.
The MPEG mod version of VirtualDub is a good, free tool for this type of job.
Either of the two above answers will satisfy your needs, depending on what you have (software version and also in the way of a DVD). If you would like a bit more background on .VOB's, this ARTICLE might give you some insight.
Harm made mention of the 100% DVD-compatibility. That can be a big gotcha, with some DVD's. Then, some form of ripping of the DVD is usually the only recourse. That is where Jim's rec. comes in.