I'm looking to do the same thing between two accounts on the same mac.
However now I've created a problem that I don't know how to fix. I simply tried to move the address book in account #1 to the users>shared folder. Address book then shows up in the users>shared folder of account #2 but it's simply the account #2's address book. Go to account #1 and the address book in the users>shared folder is account #1's address book. Now I can't get the address book out of the shared folder of either account. I get a warning saying it can't be deleted because address book is being used. However the address book application in both accounts is not open when I get the warning.
So first how do I get back to not having the address book in the users>shared folder and second how do I move the address data from account #1 to account #2?