Exchange maintains two primary address books. The Global Address Book is a listing all of mailbox users and message storage containers maintained on the SPU Exchange Server. This is usually the "default" directory used in Outlook 2003/2007 or in Webmail when you want to check an email address.
If you have stored Personal Addresses in Webmail or Outlook, they are stored in your Contacts folder.
The default Address Book, plus any secondary address books can be modified within Outlook 2003/2007.
In the main Outlook window (as opposed to in a new message), go to the Tools -> E-mail Accounts. Select View or change existing directories or address books and click Next . To make your contacts show up in the Outlook Address Book, select Additional Address Books -> Next, select Outlook Address Book ->Next -> OK.
Close and restart Outlook.