Jeff Gilbert recently wrote a great blog on an issue that was found regarding the schema extension with SCCM.  The intro is below and you can read the entire post at http://myitforum.com/cs2/blogs/jgilbert/archive/2007/09/29/upgrading-sms-2003-active-directory-schema-extensions-for-configuration-manager-2007.aspx.

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I'm posting this information because we've found an issue with a method of extending the Active Directory schema for Configuration Manager and I won't be able to officially document this until the next documentation release which is still a few months off (this information has been added to the Configuration Manager Documentation Library, but it won't be available until the next documentation update). This issue was also identified by Stuart James who posted this excellent article on myITforum earlier today: http://www.myitforum.com/articles/42/view.asp?id=10804

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J.C. Hornbeck