Adding an existing library
If you have an iPhoto library already on your disk, you can add it to your list by clicking the "Add Library" button or selecting “Add Library” from the File menu. iPhoto Library Manager will automatically search your computer using Spotlight for any libraries that are not already in your library list. You can select one or more libraries from the list it displays and then click “Add” to add those libraries to your library list.
Spotlight is not able to search some drives, such as network drives or other drives excluded from Spotlight indexing. If a library you want to add does not appear in the list, click the “Choose Manually…” button, and that will let you select a specific library to add to the list.