See http://www.slipstick.com/addins/contacts.htm#dupes

Signature
Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Is there a way, within Outlook, to compare multiple users contact lists for
> duplications or variances? At one time there was an add-on program that did
> this, but I was told by a user that Microsoft had added the compare feature
> to Outlook 2003.