Open Outlook 2007 as you would normally
Access the “Tools” menu and select “Account Settings ...”
Ensure that “Microsoft Exchange” is selected and click the button marked “Change...” just above and to the right of it.
Click on “More Settings ...” at the bottom right.
Select the “Advanced” tab (second from the left).
Click on the “Add...” button in the “Mailboxes” group at the top.
Enter the email address for the mailbox you wish to add and click “OK” on this dialog.
Providing you have entered the details correctly the new mailbox will be displayed under “Open these additional mailboxes” in the dialog. If you have additional mailboxes to add you can click on “Add ...” again and repeat the previous step.
When you’ve added all the mailboxes you require click “OK”.
The “Next” button at the bottom right will now be available on this dialog. Click “Next”.
The shared mailbox will now be available.