Uhh, many people have tried this (heck i wanted to use an air-cond rad)
but it's inefficient to many extents. plus, your pump would not be able to efficiently circulate water thru it, and hence your temps will probably be higher than your air cooled proc.
it's gonna be pretty hard to attach it to anywhere too dont ya think? car rads are pretty darn huge, and getting a silent fan that can push a decent amount of CFM through that dense copper fins is gonna be tough.