Physx with my 5830 x58 mobo

Hello, I am curious about physx , in metro 2033 in game settings it shows that I can turn it on even though I have an ati card. Same with mafia 2, does it do anything when I enable it? Does ATI have some type of physx as well? Also I am wanting to get a physx card to put in my system just to mess around with, how can I tell if I am able to do that with my motherboard, I have a GA-X58A-UD3R gigabyte motherboard with a radeon 5830, my mobo has 4 pci-e slots so im hoping I can use a physx card. Also I have read that you need hacked drivers to be able to do it but I have seen some games with system recommendations with an ati card and nvidia card for physx.

Any input would be great.

Thank you.