there is a little tool you can get from the part store (rent or buy either one) called a stud extractor kit (they also carry bolt off kits, and screw out kits) you would use this as long as its broke off outside the motor [i.e. where theres still something for it to grab onto.] i did this on my old integra the ghetto way before i new about that tool, i took the manifold of use a small pair of locking pliers (aka vise grips) and just broke it loose that way.
or if it broke off in the motor you can try one of two things either drill a tiny hole in the rnd of it and try to use a screw style extractor or you can drill out the whole thing and do whats called a heela coil (spelling?) thats about it.
