Installing Exchange 2007 Service pack 2 on a Windows 2008 SBS generates an error, as detailed here:
http://support.microsoft.com/kb/973862.

To resolve, you can either follow the instructions outlined in the KB, or you can download the installation tool, especially designed for SBS 2008.

1. First, download these:
   • Exchange 2007 SP2 (64-bit edition):
     - http://www.microsoft.com/downloads/en/details.aspx?FamilyID=4C4BD2A3-5E50-42B0-8BBB-2CC9AFE3216A
   • Exchange 2007 SP2 installation tool for SBS 2008:
     - http://www.microsoft.com/downloads/en/details.aspx?FamilyID=FFD2FE61-9278-489E-9B96-3816394C9CB6
2. Run the first file to extract its contents to a folder of your choice. Do not run the installer!
3. Run the second file to install the tool and run it. When asked for the files of Service pack 2, point to the folder where you extracted the SP2 files. Follow the on-screen instructions, and wait for the installation to complete. Do not close the installer tool until SP2 is completely installed.
4. Optionally, you can remove the installer tool once it's completed.

Notice

As SBS 2008 is always 64-bit, download the 64-bit edition of Exchange 2007 Service pack 2.

What the tool does

The tool prepares the SBS 2008 for the installation of SP2 by turning off various auxiliary services (including Forefront Security), installing the service pack, then turning them back on. When not using the tool, the installation of SP2 will fail because of safety tripwires in the Exchange SP2 installer. A more detailed explanation is outlined in the KB: http://support.microsoft.com/kb/973862.