You're not going to be able to do this from the PS3. Blu Ray movies have fairly strong encryption, and the only decryption program available that is effective against it right now is AnyDVD HD. This program will only run on a PC using a Windows operating system.
So, you'll need a blu ray drive in a pc, AnyDVDHD and a lot of space on your hard drive. You can save to an external drive, but then you have the problem of playback. Some of the software programs that can play Blu Ray will not play from files saved on the hard drive (PowerDVD for example). Some others, like ArcSoft Total Media Theater can still do this. Media companies have instituted these restrictions, so I'm not sure how Arcsoft is still getting away with this.
You can save the blu ray movies as ISO files, and mount them in a virtual drive. All the software media players with blu ray support will play them when done this way.