As damric requested, i will do a simple tutorial on how to do the PhysX hack,
1. look here and see if your card is supported:
http://www.nvidia.com/object/win7-winvista-64bit-258.96-whql-driver.html
2. download the v1.005ff hack here:
http://www.ngohq.com/graphic-cards/17706-hybrid-physx-mod-v1-03-v1-05ff.html
3. download the latest PhysX Driver that is working from the same website above.
4. install your nvidia card into your system ( if you haven't already)
5. install the display driver first, it may say PhysX driver failed to install, but just ignore it and DO NOT click on the restart button yet. Then install the PhysX driver downloaded from the website on step 2, if it says there is a newer driver installed already, use the Windows program remover thingy( the built in program remover) to remove the one that is already installed, DO NOT use driver sweeper because you will need to restart before it will actually delete it, then you should be able to install the downloaded one.
6. open the hack, and click on the .exe file in the rar. and click on apply at the bottom left of the app. once it's done shutdown the PC.
7. once the pc is off, unplug the monitor cable and plug it into the nvidia card, once windows loads open NVIDIA Control Panel.
8. Look for the option that says PhysX and change it to the Nvidia GPU if it isn't already set.
9. shutdown and plug monitor cable back into AMD card.
10. turn on PC and open GPU-Z and check if PhysX is enabled, and use FluidMark to test it.
Note: I am still trying to find a way to flash my card into a 400 series,(probably a 460) because the Nvidia Driver 258.96 doesn't not support the 550ti. and the 267.59 doesn't work properly.
EDIT: Credits goes to the person
HERE and
HERE i just explained it better.