Pci-ex is backwards compatible, so 3.0 cards will work in 2.0 motherboards. What might be an issue is motherboard bios compatibility. You've provided very little information on your computer but just from the "p43" part I know it's old. So you might be better off buying an older used card. Something from the GTX 6xx series would be guaranteed to work, provided you have the power supply for it.