I've got a 17" iMac G5 on which I enabled the screen spanning hack to be able to use a second display in extended desktop mode. I've now moved and need to go back to just one display due to space restrictions. No second display is connected, but the iMac still thinks one is, which creates a lot of annoyances. I don't see any options in System Preferences to simply turn the second display (which isn't even plugged in) off. ?