There are legal DVD ripping software -- they won't copy copy-protected stuff. But turning DVDs into iPod video usually is not a one-step process. There are free tools out there, but often than not they require many steps. First you need to "rip" your DVD, then you need to turn the .vob files (basically mpeg2) into the appropriate iPod resolutions and formats (.mov, .mp4, etc.)
What platform do you have? I use the Mac, and I have MacTheRipper (free) and VisualHub (also free, but discontinued, unfortunately). Great programs. On the PC, I think there's also a version of VisualHub and tons and tons of ripping software.
Check out
www.dvdrhelp.com. Lots of information and links to software. In particular, follow this
link.