You need to decrypt the dvds in order to copy them or transcode them to another format.
To do this use an up to date decryption/ripping program. I suggest getting DVDFab HD Decrypter. It is free to download and use. http://www.dvdfab.com/free.htm
Be aware that as you use this free section, you will be using up the free trial of the main program, but the free decryption/ripping section will continue to work even after the 30 day trial is finished.
If you want the dvds in their original format, you just have to use this program and copy the movies onto the external drive. They will take a lot of room this way, so you may just want to rip only the main movie rather than all the extras. There is an option to do this with DVDFab HD Decrypter.
If you want them in even smaller sizes, you can use the program that Macrovision linked to make them into xvid avi files. (convert the ripped dvds and save them to the external drive). This will take a fair amount of time to convert. There are lots of different programs that can do this conversion...Xvid4PSP is just one. Lots of people use AutoGK.