I do not have access to a Windows 2008 server but I typed this string into a Google search box:
remote desktop group policy "windows server 2008"
This got me a number of hits such as this one:
http://technet.microsoft.com/en-us/library/ee791928%28WS.10%29.aspx
Group Policy Settings for Remote Desktop Services in Windows Server 2008 R2which has a number of further links to follow.