There are so many wiki's out there on how to do this. Do a google search for ripping dvds and see what comes up. Also remember that a lot of DVD's have copyright protection on them so it's not as simple as just "ripping" them.
I'm sure there are 1,001 ways to do this but I used PocketDVD Studio with my pda prior to buying a BB. I had a Dell Axim PDA so I used pocketdvd to copy dvd's to a wmv or avi file. It could open and copy dvds, ripped dvd files, and any video files. So I would just use that to make copy a dvd. After I use that, I just use Desktop Manager to put it on my BB. I'm sure there are other and one-step ways to do this but just thought I'd share my experience.
