It's the little plug/screw thing on the bottom of the radiator that you loosen to drain the coolant. White plastic screw thing with a black thing around it with a little rubber hose. Do you think Autozone would have one, or would I have to get one from a Nissan dealership? I snapped the screw part.

 

I think you are talking about the radiator drain **** or petcock.
Dealer would sell you a whole new radiator along with about every place else unless you bring in the piece and try matching it with the one's in the "HELP!" section