Cannot use Outlook 2003 address book

[Alfred Einstein]

I had to reinstall Windows XP and Office 2003 after a disk crash. But I had
a backup of my .pst file, so I was able to recover all my mail and contacts.

But now, when I create a new mail message and click the To... button, I get
this error:
The address list could not be displayed. The Contacts folder
associated with this address list could not be opened; it may
have been moved or deleted, or you do not have permissions.

All my Contacts are there in the Contacts tab. Why won't they show up in the
so-called Address Book?

And what is the difference between Address Book and Contacts, anyway?