PCI-Express Questions!!!!

I'm running some random motherboard that came with my gateway dx4300-03, and i want to upgrade my GPU to an ATI Radeon 5670.
Here is my computer specs
http://reviews.cnet.com/desktops/gateway-dx4300-03/4507...;subnav

My problem is that my motherboard only has slots for PCI-Express 1x and PCI Express x16, but the card I want needs a PCI-Express 2.1 (x16) slot


http://www.tigerdirect.com/applications/SearchTools/ite... is the card I want

I really don't want to have to waste money on that if is not compatible with my computer.

Somebody please help!!!!