Download NVIDIA PhysX System Software, this update is compatible with AGEIA PhysX processors and software runtimes.
This driver Supports all AGEIA PhysX Processors and GeForce PhysX. This driver will allow you to select and dedicate a GPU to PhysX as well.
This PhysX driver is bundled in the 177.83 WHQL Drivers which can be found here:
GeForce ForceWare 177.83 XP (32-bit) GeForce ForceWare 177.83 XP (64-bit) GeForce ForceWare 177.83 Vista (64-bit) GeForce ForceWare 177.83 Vista (32-bit)
We have an article ready explaining GeForce PhysX right here.