There are serveral question related to WIN2008 and .NET support and i think these are the short but clear answer to see

• Windows Server Core – No .NET Framework (Ever!)
• Windows Server with no roles - .NET Framework 2.0
• Windows Server app server or web server roles (not listing the specific ones) - .NET Framework 3.0
• .NET 3.5 is supported (and encouraged) on Windows Server 2008, but it is a download after the fact.