Outlook (2003) email bug following Xp SP2 install

We have recently installed XP SP2 on PC’s we discovered were lacking.

We have received 2 reports so far (confirmed)that incoming (internal/external) email does not appear in the Inbox until triggered by another event, such as opening an existing message.

Has anyone come across this, and know the cause/fix?

Our email server is Exchange 2000/windows 2000