Outlook is not suitable to automate from a service. You can try using CDO 1.21 instead, but it is much more difficult to create a contact; see http://www.cdolive.com/cdo10.htm for some of the fields involved.

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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
>I want to run a window service which collects the list of contacts from a
> oracle database and updates to outlook contacts periodically.
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>
> Thanks