I struggled with LDAP support with Outlook 2000/XP and finally gave up.
I needed a read only corporate address book that would be available when a user created a new email and clicked on the button.
I finally created a personal address book, added a batch file to copy it from the server to a local directory on the PC during the login script to keep it up to date, and then setup all the PC's to use it as their primary address book.
It isn't ideal, but it works and I can update the corporate address book by just replacing one file on the server and users get the update the next time they login!!!