Outlook 2003 slower than O2K getting messages from Exchange

We have started to deploy Outlook 2003 and the users have been quick to
identify that it's slower at retreiving messages than their old Outlook 2000.
It can take over a minute longer before messages are received by Outlook
2003, while a 200 client gets messages instantly.

Is there a client or server setting we could tweak to correct this?
CJ.