If not copy protected then yes.
You may have to use a third-party conversion program like the free HabndBrake program to convert them to a compatible format.
Sorry, but if you're referring to commercial and hence copy-protected video DVDs, breaking the copy protection, which would be necessary to copy the videos from the DVD and convert them, is illegal in the US (and other countries) and hence Apple explicitly forbids such posts. We're therefore not allowed to discuss it here.
If these are home movies that you or someone has burned to DVD and hence are not copy-protected, Handbrake (freeware) is one of the more popular converters. Once converted, you just drag the movie into the iTunes window on your computer.