JSI Tip 9126. Incorrect Schema extention for Mac OSX prevents ForestPrep from completing in Windows 2000?

Microsoft Knowledge Base Article 887426 contains the following summary:

Some administrators who implemented Active Directory Schema extensions for Mac OSX may have unintentionally used a registered object identifier. This can cause ForestPrep to fail if you try to upgrade to Windows Server 2003. This article describes the steps that you must follow to resolve this issue.