When I use env_fog in a map, I just get an entire screen full of whatever colour the fog it is set to. You cant see anything through it...nothing at all. Making any sort of change to the distances makes no difference either. Even if I set the fog to start at 5000 from the player and end at 10000...I still have a full white(or whatever colour) screen.
I run HL with openGL set as the renderer...I have a 64MB Radeon7000 series...which has open GL and is working. (according to the advanced display properties all OpenGL functions are correct)
If I run the old Spirit demo map, I encounter the same problem and the on screen text says that if the screen is full of the fog colour then you are not running in openGL but I am ??