Here's a couple links I think will help ya out. The first is a how-to on using DVD decrypter and DVD shrink. The other 2 are downloads for the programs. Basically you decrypt the file in DVD decrypter then shrink it in dvd shrink then turn around and burn it in dvd decrypter. If your libarary of movies starts getting to big your gonna have to start burning them. Not only that there would be nothing worse than loosing a terabyte of movies hard drives don't last forever and accidents do happen. I lost 40gigs of music cause somebody tripped over the wire from the external drive to the computer.
Consumed Consumer . org: HOWTO: Back-up your DVD for free
DVD Decrypter
Download DVD Shrink 3.2.0.15 - DVD Shrink - A FREE software to backup DVD disks ! - Softpedia