The low (by current standards) ram on the graphics card might be the problem.
Clear Skies is one of 2 games I can't max out at 19x12, it's a pretty demanding game.
I'd recommend setting all settings to their lowest, and start from there. Build up bit by bit, and see how your FPS fares. You may need to keep textures towards the low end, as the game may need 512MB or 1GB vram for the larger textures.
June 4, 2010 4:31:17 PM
I would suggest changing from the 1.5.10 version to the "Clear Sky Complete" version. It fixes a lot of video problems from the previous versions. It is considered a mod, so it hasn't been released by Steam yet, but it is available on the net, just look for "Clear Sky Complete", download the update, install it with the provided instructions, and you should be good to go.