http://www.aa1car.com/library/overheat.htm
That link pretty well covers causes and cures for overheating.
http://www.misterfixit.com/headgskt.htm
That link tells how to test for a blown head gasket, see the paragraphs 5, 6 & 7.
Also has a simple test to determine which head or cylinder is leaking so you don't have to pull both heads.
Best not be driving it overheating because you could crack a head, engine block or cylinder wall.
Good luck and I hope your repair bill isn't to expensive.