Here is the motherboard, if it helps:
http://support.gateway.com/s//MOTHERBD/FIC/105554/105554nv.shtml
It says there are 2 PCI slots, one PCIe x1, and one PCIe x16. It doesn't say what revision the x16 slot is, but I'm assuming it's either 1.0, 1.0a, or 1.1 due to the age of the computer...