SAP Recommendation for OS Upgrade - Windows 2003 to Windows 2008

Dear Experts,

Could you kindly telling me if I upgrade the Operation System from Windows Server 2003 Enterprise x64 Edition to Windows Server 2008 Enterprise x64 Edition I need to make a Homogeneous System Copy or Heterogeneous System Copy? What´s the SAP recommendation for SAP ERP product in this case?

Best Regards,

Samuel