As far as I can tell, it is trivial to enable multiple simultaneous remote desktop sessions for Windows Server 2008.

• Open gpedit.msc
• Navigate to Computer Configuration -> Administrative Templates -> Windows Components -> Remote Desktop Services -> Remote Desktop Session Host -> Connections
• Double-click “Restrict Remote Desktop Services users to a single Remote Desktop Services session
• Check “Disabled” and apply.

There is one caveat, however. It seems to leave a Console session active at all times. You can log off the Console session via Task Manager. If you connect to it (by right-clicking it in task manager) it doesn’t seem to be doing anything.