and any hard drive for your computer. Use your computer to format the drive as FAT32. Now move the dock & drive over to the PS3 and connect it via USB. Now, select a movie and hit the triangle button. If you have the option to copy, selct it, then select the USB drive as the destination.
Now you can move the dock and drive back to your computer.
Most movies are copy protected and will not allow you to copy them off the PS3 system drive.