In theory the gt620 should work with pciex8, even the pciex4, because the pcie is backward compatible. But that dell has the intel e7230 chipset, it is old, I don't have time now, you may go to dell support to see there is any newer version BIOS. If the dell does support the newer BIOS like after 2009 or 2010 version, you should be fine, because the MB usually needs the BIOS to recognize the new hardware.