Depending on what format the video is in to start with you can chose from these programs:
HandBrake - You can encode straight from DVD to iPhone .mp4 format.
VisualHub - You can encode AVI's, MKV's etc etc... into iPhone .mp4 format.
QT Pro (With Perian) - Any codec that plays in QT Pro will exprt to iPhone .mp4 format.
iTunes - Any .mp4 already in iTunes you right click on the video and the click convert selcection to iPod/iPhone
I think those are the only choices. Hope it helps you and/or someone else
Northy