Yes, I believe that you can. You will need to change the Owner/Group/Permissions to allow BOTH users to READ/WRITE/EXECUTE to the address book file (and its parent folder if it also not otherwise accessable to the other user -- otherwise they have no way of getting to it). If "Show Info" cannot solve your problems (it doesn't allow you to change Owners, for example), try "Super Get Info" or "XRay" (my new favorite).
At http://j2anywhere.com are a number of tools and instruction manual which cover the configuration of a shared LDAP server. The tools on the site allow you to transfer contacts from your AddressBook directly to the LDAP directory, which can be accessed by Mail and the Addressbook. LDAP also supports other platforms such as Windows and Linux and is supported by many mail clients and addressbooks.
You will also find AddressBook X LDAP which is currently in BETA and provides a iSync integration.