Turn off the reminder in the meeting requests you send from Outlook 2003. If that works, then you'll know that you need the hotfix for Outlook 2000 described at http://support.microsoft.com/?kbid=823199
Outlook 2003 does not have any peer-to-peer sharing capability. See http://www.slipstick.com/outlook/share.htm for possible solutions.

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Sue Mosher, Outlook MVP
Outlook and Exchange solutions at http://www.slipstick.com
Author of
Microsoft Outlook Programming: Jumpstart
for Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Is outlook 2003 compatible with previous versions of
> outlook. I have sent meeting notices from the calendar to
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> worked with Outlook 2000. I am concerned that Outlook
> 2003 is not compatible with 2000.