I have this kind of problems with ATI, disregarding the driver version i change, old, new ... from ATI, from Omega...
This problems was present into a X800 XL, X800 XT, X800 XT PE, and even into a X850 XT... finally i decide to stay with the X800 XT PE... not to much performance diference with X850 XT, and lot of low price... in that age i buyed this card.
This problem is present into SH III, SH IV, IL-2 all saga.... plus into the U-Imperial Flottilla pre alpha by Deamon from this forum.
Nothing seems to fix this problem, i tryied all settings into the driver control panel and ingame settings.
The only thing wich seems to avoid it was to underclock the default settings. W XP is up to date, Dx is up to date. Omega drivers seems to help a lot.
But it happens into 4 diferent card models, X800 XL, X800 XT, X800 XT PE, and X850 XT.
I didnt experience it into SH IV up to patch V1.2 was out...
