Check under your oil cap and see if it looks like a milk shake. If so, blown head gasket. If not, let it warm up and using a couple of fingers (be careful) touch the radiator every few inches over the whole thing. It should be evenly hot over the whole thing. If you find a cool spot, or spots, then you're radiator is plugged up. You can have it gone through at a radiator shop, but it seems like that's usually a waste of money. In the long run a new radiator is your best bet.
Also check your thermastat. They're cheap and easy to swap out.
good luck