Outlook XP installation problem

I’ve just upgraded from Office 2000 to Office XP (Dutch version).However, when I now try to open Outlook, I get an error message, translated “Cannot start Microsoft Outlook. Cannot find the .DLL file of the service program. The information service PSTPRX.DLL has not been loaded by MAPI. Check if the service has been well installed and configured.”
When I click OK, I get another message: “Do you want to open the standard folder of the file system instead?” When I click Yes I only get the “My Computer” information.
I’ve already tried to run the “Analyse and Recover” option in Outlook, which didn’t help.