See the screenshot below. It shows the Windows display properties in German. I can configure a second display, although I have not connected one. So far, so good. Only it does not work: When I click on OK, then the screen flashes, but nothing changes, and the option "Windows-Desktop auf diesen Monitor erweitern" ("Extend my Windows desktop onto this monitor.") is unticked.
How do I make Windows believe that there is a second monitor? (ATI Radeon Mobility 9000)
Why I want to do this? I want to access the second screen via VNC from another computer.