Ripping DVDs and putting them onto the iPhone is very easy to do. The only program you need is HandBrake which you can get for free right here. HandBrake was just updated on February 19, 2008, so I thought I'd update this tutorial.
Once you've installed the program, insert the DVD you want to rip. Close DVD Player which, most likely, will launch automatically. Now launch HandBrake.
At the main screen of handbrake click your DVD icon, then click Open.
The DVD will now be scanned for a couple minutes.
Click the Toggle Presets button.
Select iPhone/iPod Touch from the list.
There are many options to be made in this program, I decided to change the codecs setting from the default AVC/H.264 Video / AAC Audio to MPEG-4 Video / AAC Audio. It will save a good deal of processing time.
Click the Start button.
There is a status bar at the bottom that will tell you how long this process will take. Time will vary based on the specs of your computer and the options you chose. I did this twice. The first time I used the default settings with 1 pass encoding. It resulted in a 697 megabyte file and took half an hour to rip. The second time I used 2 pass encoding. The file was 699 megabytes and took 54 minutes.
When it finishes you will get this message - "Put Down That Cocktail....Your HanBrake Encode is Done"
Launch iTunes and select File from the toolbar, then select Import...
A file browser window will open. Navigate to where you told HandBrake to save the movie and select it, then click Open.
You'll see the import progress in iTunes.
Plug in your iPhone to iTunes. Click the Video tab. Check the Sync movies box in the Movies section, then choose your movie and click Apply.
You'll see a progress bar while the movie is uploaded to the iPhone.
When it finishes, press the iPod icon on the iPhone and check out your new movie.