With only two monitors, it's not even worth it. If it's a shooter of some sort that you are playing, the crosshair will be between the two monitors, and it will be extremely hard to aim. If the monitors aren't the same size, its impossible unless you go into windowed mode and can change the window size to fit both screens, but even then that doesn't exactly help. I'd either get another monitor that is the same size as the other two, or settle with gaming on one monitor like a normal person.