activating GPU in Cycles

using blender Blender 2.61 Cycles (CUDA) + Collada 5657_blender-r43282-cmake-darwin64 on my snow leopard, Cuda enabled I can’t tweak the settings between
GPU and CPU rendering…

On this link one can read the interface I would expect also on my system

but as seen in screen shots the setting seems to be moved somewhere else …

any hint ?

any hint ?
So what happens when you select Experimental ?
Also look in User Preferences / System for more settings for recent builds (don’y know if your is current enough)