Before you install Exchange 2007 SP1 onto a Windows 2008 server you'll need ensure that prerequisites are installed, by default .NET Framework 2.0 and Microsoft Management Console (MMC) will be installed but you'll need to install Windows PowerShell.
Note: You won't need to go looking around on the Internet for PowerShell all you'll need to do is:-
Written by Daniel Kenyon-Smith
You can also install it from the command prompt by typing:-
ServerManagerCmd -i PowerShell
on a Windows 2008 Server
The TechNet document found at:-
http://technet.microsoft.com/en-us/library/bb691354.aspx
lists the procedures for installing the Exchange 2007 pre-reqs