I was stuck somewhere the other day wishing I had the full movie “Cars” on my iPhone. Surprisingly, this is not something you can presently do through iTunes. After some searching I figured out an easy way to do it for free. The two programs you’ll need are good old DVD Decrypter and WinFF. Put DVD Decryptor in IFO mode and set it not to split the .vob files by size (so it rips them to one huge 6+ GB .vob file). Then drag the .vob file onto WinFF (making sure to use the proper preset for iPhone/iPod) and click “Convert.” It’ll take a while but it works. With my first attempt there seem to be some audio/video sync issues but I’ll play around with it.
Also, see this previous post for more info about WinFF and iPhone-compatible video.
Evan Hoffman's Blog 
i downloaded the dvd decrypter and i cannot figure out how to make the vob files into one file please help
See here: http://www.aimersoft.com/rip-dvd/use-dvd-decrypter.html