I'm on a g5 mac - I've never tried to get rid of the horizon line, but I'm guessing that with realistic sky if you set haze and fog to zero you would see no line. That line is the haze and fog, just like Bryce. Just aim the camera upward with a wide angle lens (24mm or so) and you should get all sky. Also there is a swtich to turn off the ground. Click on the word scene in your scene list and turn off ground for the sky settings. The realistic skies in C5 are very nice. Also the harsh line is caused by thick haze hanging very low. I know in realistic skies you need to set the size of the scene. A more expansive scene will make haze more realistic and remove the line, since the haze will be more realistically distributed. Scott