Create a new user on the Server called 'ouraddressbook' or whatever. Exit the Server. Into Address Book on your Admin/Client machine create a new Account. Account type is CardDAV, Username and Password the same as the User you created on the Server… 'ouraddressbook' or whatever, and then enter your Server's address as text or numbers. Click creat and the rest is straight forward. Now give the set up details of that new Account to the others who want to share your 'ouraddressbook' with you.The Clients must have, I think, Mac OS 10.6 or upwards to have an Address Book that with co-operate.
You will see a new group in Address Book.
If you don't already know, do not add accounts to Address Book or iCal on the Server. Everything is Admin and Client Side. In the beginning I was also adding accounts to iCal and Address on the Server. It works fine but it is just one extra thing that could become corrupted. Let the Server 'serve' the Users you create on it.
Hit me if you have problems.