PCIe and PCIe 2.0 are the same only PCIe 2.0 is twice as fast.
PCIe 2.0 is backward compatible so any PCIe card will work in a PCIe slot. (Dont get confused with AGP!)
When your PC starts for the first time with the new card the display will look funny. Just let the PC keep starting and if a New Hardware Wizard pops up Cancel it. When the OS has finished loading go to Add/Remove Programmes in Control Panel and Remove/Uninstall the old graphics driver, Nvidia or ATI. Put in the CD you got with the new card and install the drivers for it then reboot. The OS should detect the new card and install the correct driver for it.
But Ditch999, on the nvidia website where it helps you pick the graphics card that will work on your PC it has AGP, PCI Express and PCI Express 2.0. There are extra ones I could buy if I had PCI Express 2.0 but I do not know if I have PCI Express 2.0
As long as you have a PCI Express x 16 slot any PCIe graphics card, whether it be version 1 or 2, will work in it. As I said, the only difference is that version 2 works twice as fast but its backward compatible. If you post your motherboard make and model I will tell you what version you have, or look in the manual yourself, it should say. If you dont know your motherboard download CPUZ click here and run it and it will tell you your motherboard and more!