I can confirm that the problem regarding BLUE SKY and HUD ONLY on ATI Cards using latest drivers can be solved by rolling back to 8.2 drivers.
I installed EECH according to the instructions at EECHCentral.com (with mods, patch and apache cockpit) and ended up with blue sky and HUD. After tips from this forum I rolled back to 8.2 of ATI drivers (which was a mess to accomplish).
I'm running VISTA 64, with dual 3870 (crossfire disabled) and it works. My only problem is the Apache cockpit 1.0 that still crashes when I enter the cockpit. I have palette=0 and still the game crashes.
However, I was kind disappointed by the ingame graphics when I flew my first flight. Do you think my textures or something is incorrect? Or is this game supposed to look like a 10 year old computer game? (I know the game is old, by I tought that the mods would make the game look really good
