When you create overrides for a Management Pack in Operations Manager 2007, it's a good idea to put them into a custom Management Pack instead of the Default Management Pack: For example, if you use the Exchange Management Pack, create an "Exchange Overrides
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Read the complete post at http://blogs.technet.com/momteam/archive/2007/05/02/best-practice-for-creating-overrides-for-management-packs.aspx