"PCIe 2.0 is backward and forward compatible with PCIe v1.x. Graphic cards and motherboards designed for v2.0 will be able to work with v1.1 and v1.0, and vice versa. In some rare cases it is possible that a PCI-E 2.0 card will not work correctly on a PCI-E 1.0a slot. This is only limited to certain video cards."
But since you declined specifics this is all that can be told.
This should be a fairly easy question I was just wondering if i buy a graphics card that is pci express 2.0 will it run in a standard pci express x 16 slot?