There used to be an Address Book Card menu item under the New sub menu in the File menu for all windows. This was broken recently. I have the fix in my local tree.
Fix checked in.
Build 2000010409M13: NT4, Linux/Redhat 6.0, Mac 8.5.1 Verified Fixed. Browser, Mail, Composer and Address Book all have a File|New|Address Book Card sub menu.