Replying to External HD & Photos

To save much needed space, I just baught a 120GB external hard drive to throw some shit on there to save space on my MacBook, mainly photos. I got it, hooked it up, and tossed all the photos over to the hard drive, keeping them in the same folder, and deleted them from my computer So much space has been freed up! But, I can't view the pictures through iPhoto the way I could before. I can still view them through Preview through the external HD itself, but I'd really like to be able to have it through iPhoto again. Does anyone know what to do here? There must be something to change in the Preferences but I'm not sure what. I might just end up going to a Genius Bar. Thanks for any help.