Being someone that has a dual-monitor setup, Games will generally open on your primary monitor and leave your second one alone. If the game lets you move your mouse offscreen to the other monitor, when you click something it will minimize the game, though I have set my dual-screen up so the screen acts like 2 seperate desktops, you can also set it up like a single widescreen desktop which would stretch the wallpaper and taskbar to make it act like 1 monitor, you might have dual-screen gaming that way but it would be annoying with the gap between monitors. The 3rd dual-monitor selection is "clone" which basically shows the exact same thing on each monitor, this is the same way people connect their projectors to computers. I've never seen a game support dual-monitors but I guess it could happen. I wouldn't game on dual screen because since your 1 graphics card would have to work twice as much to display the ever-changing image on both monitors. This wouldn't necessarily cut your FPS in half but it will have a bad effect on performance. This would prolly not be a problem on multi-GPU or high-end GPU systems.