first thanks for your help.
after a LOT of different test/error, I finally play 2 night without any bug with higher resolution.
If needed, I can try to give to you all more info. But, here is big picture:
With my 9800GTX+ (512MB)
screan resolution used : 1920*1080
Quality preference is set on very high
3d Resolution used : 1680*1050
All setting is on normal except for terrain detail (high), Anisotropic filtering (disable) and shadow detail on low
in the nvdia control panel I choose the option "game decide the setting" ... maybe it's called Application-Controlled
and one important think, I cannot use the last driver from Asus or Nvdia. I have to use the old driver in the cdrom buy with the card.
later I will try to optimize video, but actually the game is very nice and no lag.
overcloker ... don't try that with arma.. I try to overclock the cpu and the video card .. but the game don't like it. The video crash like "whopper_with_cheese" said.