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.
Thanks for the reply; if 15 amps would be enough, why would Radeon rate the card at higher than that? I'm just curious.