Outlook has no Global Address Book. In an Exchange environment, the user has a Global Address List, which consists of Active Directory addresses maintained on the server and an Outlook Address Book, which displays the user's contacts folders.
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. If you are using Outlook 2003, do not select the option to use Cached Exchange mode. 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.
7. (Optional) If you are using Outlook 2003 or 2007, you can now change the settings for your Exchange account to use Cached Exchange mode.

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
> GAB is GLobal Address Book, a dynamically sahred contact folder is a new
> folder created as a contact folder that is shared with another and reflects
[quoted text clipped - 14 lines]
>> > Is it possible to add a dynamically shared contact folder to my personal GAB
>> > drop down?
Lisa AGA - 20 Feb 2007 21:05 GMT
Thanks Sue, we apparently refer to the Outlook Address book as the GAB here.
I appreciate your help and clarification.
> Outlook has no Global Address Book. In an Exchange environment, the user has a Global Address List, which consists of Active Directory addresses maintained on the server and an Outlook Address Book, which displays the user's contacts folders.
>
[quoted text clipped - 32 lines]
> >> > Is it possible to add a dynamically shared contact folder to my personal GAB
> >> > drop down?