Matuus, our in-house Guru3D NVHardpage programmer stumbled into the same issue I had as well. The NVIDIA PhysX driver once install will activate itself on the GPU, and can not be disabled.
Required: Windows Vista 32-bit, GeForce G80/G92/GT200 and NV PhysX drivers
This little NV PhysX Tweaker tool will allow you to actually choose to enable or disable the PhysX driver over the GPU and if preferred, the CPU. Very simple, yet very handy.
If you have UAC enabled, you must run this software as Administrator.