I downloaded the latest PhysX version 9.10.0513 but there is no PhysX option in nVidia Control Panel. My card is a nVidia Ge-Force 8400GS.
PhysX is supported by this card but it requires to have the latest version installed as well as the driver. You will find it on the left menu of the Control Panel. It's not necessary to update the software only, the driver needs updating.