the 9500GT is a very old gpu it won't be very good in new games. You need a graphics card for any FX CPU. Using a second card for PhysX is dodgy at best and doesn't really work well. PhysX is a physics model that is exclusive to nVidia graphics cards. Not too many games use it and you can disable it if you have an AMD card. It does make for some nice visual effects (like robes blowing in the wind for example) however it isn't very wide spread.
You could use the 9500GT for now but don't expect to play many games with it. I had one in an old Athlon build running WinXP. It played starcraft 2 ok at 1440x900, but then again, starcraft 2 isn't very graphically demanding. It definitely can't handle BF3/4, or any new game.
If you have nothing else then you might as well use it but definitely replace it as soon as you can with something like a GTX 650 Ti Boost or a HD 7870 or something. If you can get a new graphics card now, then I'd highly recommend it.