I also had the same problem. I have Vista64.
For me the solution was to lower my clocks in my 8800GT. I lowered core(-50MHz) and shader clocks(-100MHz). Good thing is that they dont affect at all to my performance in IL2. Only memory clocks seems to affect and I was able to overclock the memory 40MHz.
Also I installed this hotfix.
Vista64
http://thehotfixshare.net/board/inde...&showfile=8295
Vista32
http://thehotfixshare.net/board/inde...howtopic=11094
It could have helped too.
S Antmano