Where are the Address Books stored? Exchange server?
If it is an exchange server, look into WebDAV, it allows you to
send/receive xml web service queries and it returns the appropraite
data, you can retrieve public folders, or a specific users information.
I used it to allow people to add calendar items to an exchange public
calendar, and then display it over a website using c# and asp.net
If the address books are stored in some other medium, it depends on the
vendor and if they have a way to programmatically retrieve the
information.