Replying to Dvds to hard drive

hey guys, im tryin to put a bunch of my dvd's onto my hard drive so i can watch them next year at university. im havin lots of trouble though. i've tried a couple dvd to avi programs but i have not found a good one... most seperate the file into two or three parts or screw up the size completely. wondering if anyone has a good program for this (please say if it's a free one or one you have to pay for).
+++karma for help! thanks