Running a Macbook 1.8, core 2 duo with 1GB Ram, OSX Tiger.
Ran with the options
-heapsize 512000 -dxlevel 70 -w 800 -window -novid +cl_drawmonitors 0 +r_shadowrendertotexture 0 +r_WaterDrawReflection 0
Runs really well, especally considering i don't think my graphics card is supposed to run this even under windows. I did get very strange texture warping using -dxlevel 80 but it would only be there for a couple of seconds and then go back to normal. Textures were fine under -dxlevel 70 although to be honest I don't notice a huge difference between 7 and 8 settings. Every advanced graphical setting is set to low of course. FPS seem fine however as noted below i to get a freeze in graphics every 30-50 seconds or so. It is extremely random when it happens to me but possibly due to sound. I have sound settings low as well but might see if there is a command to set it lower. Apart from the above it runs pretty well.