There is no compatibility problem; your system memory type (DDR2, DDR3 etc,)doesn't have any bearing on the memory installed in a graphics card. As long as the graphics card is the right type (PCIe - which I am sure it is) then you are fine.
FYI - The 9500GT is a low-end graphics solution, so I hope you got a good deal (<$50) and don't have the intentions of playing newer games at high resolutions.