Note – Exchange 2007 SP3 has now been released.
If you just try to run the installation it will fail as the Exchange BPA detects SBS 2008. You will get the below error:
You must update your Windows Small Business Server 2008 settings both before and after you install Exchange Server 2007 Service Pack 2 (SP2). Before installing SP2 for Exchange Server 2007, read the detailed information at http://go.microsoft.com/fwlink/?LinkId=155135.
Microsoft have released a tool for this which can be found here:
You will also need to download and extract Exchange 2007 SP2 to a folder.