John,
Perhaps there is another option. Moving your iPhoto Library Folder to the external drive and running it from there. You can also create numerous new iPhoto Libraries on the external.
MOVING iPHOTO LIBRARY FOLDER to EXTERNAL
Moving the iPhoto Library is easy.
1. Quit iPhoto
2. Go to the Pictures folder in your account (HOME). Find the iPhoto Library folder. DRAG this ENTIRE FOLDER to the destination on the external hard drive. this will COPY it to the external.
3. Now, drag the ENTIRE iPhoto Library folder that is still in your Pictures Folder to the desktop ( out of the Pictures Folder).
4. Restart iPhoto. It will ask you if you want to create a new Library or open an existing one. Choose existing and navigate to the copy you made on the external.
5. iPhoto will now open and work with the library folder on the external.
6. When you are sure everything is working you can trash the original iPhoto Library Folder on the desktop.
MULTIPLE IPHOTO LIBRARIES
Creating and switching between multiple libraries is a snap with either of these two programs
buddy/ manager
http://nofences.net/iphotoBuddy/
http://homepage.mac.com/bwebster/iphotolibrarymanager.html
Peter