I just got an extra 750GB external drive to backup some files I keep on my 500GB external. I'd like to have a copy of my iPhoto library on both drives, in case one decides to die. Copying the files once a week won't work, since the library is approaching 200GB and I just bought a 5D... Heh. Any help is appreciated. Basically I'd like to be able to import photos to two libraries at the same time, or quickly switch between them.