With difficulty, because the process of adding another user's Contacts
folder to your own address book display is somewhat involved. You will need
to be able to create -- at least temporarily -- an Outlook profile that
opens another user's mailbox as the primary mailbox. Proceed with these
steps while logged in under your own Windows account, not the other user's:

1. Create an Outlook profile that connects directly to the other user's
mailbox, not your own, and start Outlook with that profile.

2. On the Properties dialog for the other user's Contacts folder, make sure
that it's set to display in the Outlook Address Book and give it a display
name other than contacts, such as Joe's Contacts.

3. Close Outlook.

4. In Control Panel | Mail, edit the *same profile* (i.e. the one from Step
1) to change the mailbox from the other user's to your own.

5. Still working with the same profile, on the Advanced tab of the Exchange
Server service, add the other user's mailbox as a secondary mailbox.

6. Restart Outlook, and you should see the Joe's Contacts in your Outlook
Address Book as well as your own Contacts folder.