I switched the 9600 GT in my system for a 3870 X2 today, and while playing a relatively old game Final Fantasy XI, the game and computer will lag if FFXI is not the window in focus. FFXI takes up the whole screen but you can Alt/Tab to switch to other windows and you will see FFXI behind them still running. Everything was fine with the 9600 GT but now with this card the second the mouse goes over an open window over FFXI, it lags. I thought it might have something to do with 2D and 3D clocks? I used RivaTuner and forced the Core at 850 MHZ all the time so it isn't switching back and forth. What is causing this?