Heres quick tutorial on how to do this... I know many have been posted before, but I like this 'free' method
Things you need before we start.
1. handbrake for windows [
download]
http://handbrake.m0k.org/
2. dvd43 [
download]
3. a dvd you want to watch on your iphone (almost any dvd should work)
** install both handbrake and dvd43 before continuing **
STEP 1
Make sure DVD43 is running, you can tell by a smiley face in your system tray. It may be yellow or green.
STEP 2
Insert the dvd you select. (ones you own please

)
STEP 3
Start Handbrake
STEP 4
Select the DVD Source : it should be your DVD drive
** it will say "Reading DVD..." leave the screen open, it will close itself **
STEP 5
DVD TItle: Automatic
DVD Chapters: Automatic
Destination: c

(change to where ever you want) - This is where the mp4 will be stored once its completed, you will also need to select a file name.
Encoder: H.264 (ipod)
Audio Encoder: AAC
Width/Height: (i leave blank)
** you can play around with the other settings, but this is all i need to get it done **
STEP 6
Press the Encode Video button (bottom right corner)
** this will open up a cmd window in your start menu bar, make sure you look for it, it will give you the time remaining on the encoding **
Thats it, and your done! copy that to itunes and all your videos can now be in your iphone or ipod for that matter.
If your wondering what DVD43 is for, its an on the fly dvd decrypter which can remove some protection the disk may have.
Disclaimer:
Remember this is for your own personal use as a backup incase your CD gets damaged or what not. this is not intended to be used with services like blockbuster or netflix. Heaven forbid... that would be wrong!