3D game problem

Hi,
even though my system setup is quite good, I have some problems in the 3D mode. The game is really slow, even though I am playing without any shadows and spectators. Furthermore, I am always recommended to play with the lowest graphic settings possible.
Does anybody know, what I can do to change this?
Here is my current system setup:
Windows Vista SP2 - 32 bit
Intel Core 2 Duo CPU 2.67 GHz
3 GB RAM
NVIDIA GeForce 8600 GS (driver date: 20.05.2011)
DirectX 11
even though my system setup is quite good, I have some problems in the 3D mode. The game is really slow, even though I am playing without any shadows and spectators. Furthermore, I am always recommended to play with the lowest graphic settings possible.
Does anybody know, what I can do to change this?
Here is my current system setup:
Windows Vista SP2 - 32 bit
Intel Core 2 Duo CPU 2.67 GHz
3 GB RAM
NVIDIA GeForce 8600 GS (driver date: 20.05.2011)
DirectX 11