Every now and then something actually useful lands in my Inbox and my thanks goes to MarkS in the UK GTSC for sending this on. I think it explains itself :)
Grab the security hot-fixes for the operating system from http://www.microsoft.com/technet/security/current.aspx.
Exchange 2007 Requirements
If you are going to install Exchange 2007, you will also need these fixes:
If the Operating System is Windows Server 2003 SP1:
In addition, if you are going to install Exchange 2007 Unified Messaging role, you will also need these fixes:
In addition, if you are going to install Exchange 2007 Edge Transport role, you will need:
If still using Windows Server 2003 SP1, then install these hot-fixes.
Install the cluster-specific Post-SP1 hot-fixes on cluster servers - http://support.microsoft.com/?id=923830
Grab these Windows Server 2003 Post-SP1 hot-fixes:
Cluster specific fixes