Not really. There's a very limited Rule.dll that requires CDO 1.21 and can create only server-based rules that are not visible to the user (and so likely to cause confusion).
Outlook 2007 will have full rules support in the Outlook object model.
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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers