it really depends on a few things. are you trying to do the easiest way? or the cheapest way? the easiest way in my opinion is SPB dvd mobile. you drop the dvd into drive and pick what parts of the movie and what size. it does the rest.it plays on coreplayer or the built in windows media playeryou can buy it here
http://www.spbsoftwarehouse.com/products/mobiledvd/?en
the cheapest way is to use a program like dvd shrink, it will give you vob. files then use a program to convert it to a avi