New MacBook user. Formerly used Lightroom on my PC to organize digital pics, but have used iPhoto since purchasing the MacBook. Now, at a point where I want to move my iPhoto library from the MacBook harddrive and start using my external USB drive (via the AirPort Extreme). I would also like to import the pictures I already had on this external drive into iPhoto so that all my pictures are in one spot, and are able to be accessed through iPhoto via the AirPort. So to sum, want to move files from MacBook to external drive, merge them with already existing files, and use iPhoto to manage them all. Did that make sense? What's the best way to accomplish this?