There are additional steps to get Exchange 2007 SP2 installed on SBS 2008, below are the steps to complete from Microsoft Support
http://support.microsoft.com/default.aspx?scid=kb;EN-US;973862
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There are additional steps to get Exchange 2007 SP2 installed on SBS 2008, below are the steps to complete from Microsoft Support
http://support.microsoft.com/default.aspx?scid=kb;EN-US;973862