First you need a drive formatted Mac OS extended (journaled) with permissions ignored
Or to share amoung users with iPhoto running but the library not on a seperate drive see http://support.apple.com/kb/PH2435
we want to be able to have multiple users viewing the same iPhoto Library?
Do you need to have the multiple users to be able to edit and otherwise manage the photos or just view them?
If it's the latter take a look at Media Pro 1. It's a multiuser and cross platform digital asset management application. With it you store your source files on a server along with the catalog file that Media Pro uses to manage the photos. One user can manage the catalog file while unlimited others can view the file in read only mode with the Media Pro Reader. You can learn more about MP1 at DAM_Forum The DAM Forum
It's a professional and more robust system of managing photos than iPhoto is.
Excellent thanks for all this information everyone.
If you view photos from a shared photo library can you edit them? or only view them?
Yeah we need to be able to have multiple people editing and viewing the photos. We may have to stick with only one person viewing the library at any one time. Just gets a bit annoying when 3 people are wanting to see the same library at the same time.