Darkstream , you might want to try that sky Mod :
http://www.subsim.com/subsim_files/p...20mod%20V2.rar
I myself run a Radeon X800 GTO from GeCube ~cheap and kick-ass card~ and never had a problem .
On the other hand , you could try to raise your anisotropic filtering to x2 or even x4 if your 8500 is up to it . It sometimes help with "flickering" textures .
Good luck .
Cheers .