Now now ladies, lets not start a PC vs Mac war.
Isseth: Try unticking the following;
-Fluid Blood
-Reflections
-Soft Shadows
-Ambient Occlusion
-Bump-mapping
-Raytracing
Then tick Shaders, and see how you go from there.
Well first of all make sure your graphics card has shader model 2.0 or higher, if not toribash will always turn shaders off again, if it does and it still doesn't work update your video card's drivers.