Currently Being ModeratedApr 18, 2013 2:49 PM (in response to Ron73)
You need to move it as an unit. While it isn't actually an unit, moving or copying it piecemeal will result in a damaged library unless all the parts of it are in place before attempting to access it in iPhoto.
Currently Being ModeratedApr 18, 2013 2:59 PM (in response to Ron73)
To move a Library to an external disk:
Make sure the drive is formatted Mac OS Extended (Journaled)
1. Quit iPhoto
2. Copy the iPhoto Library from your Pictures Folder to the External Disk.
3. Hold down the option (or alt) key while launching iPhoto. From the resulting menu select 'Choose Library' and navigate to the new location. From that point on this will be the default location of your library.
4. Test the library and when you're sure all is well, trash the one on your internal HD to free up space.