First of all, I know absolutely nothing about computing. I have no idea how to build a computer, I don't know what a RAM is and I don't know the difference between a Sapphire HD 5770 1GB GDDR5 Dual DVI HDMI DisplayPort HDCP PCI-E and a ATI Radeon HD 4770, heck I don't even know what they do.
Now... I'm looking to purchase a new computer, something that can get around 20 fps in a 25 man on high-ish to ultra video settings. When I walk into the store, what system specifications (I have no idea if that is the right term) am I looking for or what do I tell the clerk at the store?