crucial

VOB is a container file format used in DVDs. Here is how to get this into an iMovie editable form or to get it ready for quicktime or flash video conversion.

DivA
http://diva.3ivx.com/

will convert the VOB to an AVI or MOV. remember to set the aspect ratio correctly, it assumes it is working with widescreen films.
There will be no sound track.

bbDEMUX
http://sourceforge.net/projects/macbbdemux

de-muxes the VOB file : splits it into its component parts of video, soundtrack(s), subtitle(s) etc. use this to get the soundtrack files. These will possibly/probably be an ac3.

mAC3dec
http://sourceforge.net/projects/mac3dec/

will convert the ac3 audio file to an AIFF

Use Final Cut Pro or iMovie to put the video and soundtrack files together again. It should be quite easy using iMovie. With FCP, not so much.