Choose the library you want to copy and choose 'Reveal Library in Finder' from the File menu.iPhoto Library Manager will copy the library and, when it's done, it will automatically appear in your library list. You will be prompted to choose a location to store the new copy of the library. Choose the library you want to copy and choose the 'Duplicate Library' command from the File menu.
If you want to make an exact copy of one of your libraries, either as a backup or as part of moving a library to another disk, you can do so one of two ways.