Gigabyte G31M-ES2L..HELP!!!!!!!!!1

HELLO FRIENDS,
i have a gigabyte G31M-ES2L rev 1.0,
i was using the inbuilt intel graphics accelerator g31 series but i want to move on and get a upgrade for my graphics card.
so i thought i would go for a Nvidia GTS 250 or 240 or nvidia 9600gt.
but my mobo have only PSI express *16 slot, but all cards require PCI express 2.0 *16 slot.
and all above mentioned cards are DDR3 or DDR5 but my mobo retailer says that "my mobo won't support DDR3 or DDR5 cards".
please help me by giving any kind of suggestion or tips etc.
thanks in advance.