Here's how I'm doing it:
1. Rip the DVD with Mac The Ripper, the files are placed on your hard drive.
2. Use HandBrake to convert the ripped DVD into a MP2 encoded with H.264.
3. Import the MP4 into iTunes.
4. Sync your iPhone and you have the DVD on it.
Have have a break down of doing this a few ways at:
http://www.teachlinux.com:8080/iPhone
If you have an iPhone just go to
http://www.teachlinux.com:8080 the website will format it so your iPhone likes the site.
HtH,
Denis