After installing Internet Explorer 8 on a Windows Server 2008 Terminal Server the Internet Explorer Enhanced Security Configuration is set to on for all users and can't be switched of via Server Manager.
Solution
Use a GPO registry preference to force the REG_DWORD IEHarden to 0 under HKCU\Software\Microsoft\Windows\Current Version\Internet Settings\Zone map\.
Source: Windows Server TechCenter > Windows Server Forums > Windows Server 2008 R2 General - Read Only > Cannot disable IE Enhanced Security Configuration after installing IE8 via Windows Server TechCenter > Windows Server Forums > Group Policy > Win2k8 Terminal Server losing GPO Settings Re: Site to zone list