Probably you have to change your display settings in Windows.
Right click on your desktop and press the "Properties" menu item, then click on the "Settings" tab and on the "Advanced" button.
In the new window, click on the (last?) tab regarding your Video card.
Now you have to search for multidisplay options and change the settings appropriately, search for nView settings (since I don't have your Video card I don't know what you have to do exactly, maybe you'd better chack the Video card manual to know what to change)
