Cause iPod can play only MP4 format video, DVD movie is MPEG-2 format, in order to put it on iPod, you have to rip your DVD movie to MP4 format. I always use Wondershare DVD to iPod Ripper to do that, my friends recommend it to me, so easy to use and works great for me. This software can rip encrypted DVD movie to iPod format. what you need to do just put your DVD disk on your DVD-Rom and start conversion, then this software will help you transfer the DVD to iPod directly wihout iTunes, really help. Here is a step by step guide about this software
http://www.dvd-ripper-copy.com/forum/viewtopic .php?t=6
you can download the software free from here
http://www.dvd-ripper-copy.com/download/dvd-iP od-download.html
I hope it helps.