The Microsoft TechNet site is a starting point for Windows security resources.
The Windows Server Security page provides security guidance topics for the Windows Server operating system in general. The page is located at: http://technet.microsoft.com/en-us/windowsserver/ff843381
The Secure Windows Server page provides security topics that are specific to the Windows Server 2008 operating system. The page is located at: http://technet.microsoft.com/library/dd548350%28WS.10%29.aspx
For example, one of the security resources from Secure Windows Server page is the Threats and Countermeasures Guide.
You can use the Microsoft Security Compliance Manager, which includes extensive guidelines and documentation about hardening the server. You can download the manager from: http://www.microsoft.com/en-us/download/details.aspx?id=16776