Drill a small hole right in the center and use an easy-out to extract it if its countersunk in a little, remember to run a thread tap in afterwards incase it messed a few threads up. if its realy tight and wont budge take your rear main seal off and heat the crank up a little with a propane torch or somthing (nothing to hot) just get it fairly warm then use an air nossel and spray some compressed air onto the snapped off bit quick and try with the easy out again, normaly it helps it loosen up a bit.
As far as a stripped nut that wont back off, try heating it a little aswell if possible and try wedge somthing underneeth it to forse it up off the bad threads as you are undoing it or just unscrew the hole stud its screwed into cause the chances are they are dammaged
If you cant get it right go here:
http://www.highspeedperf.com/Pages/Contact/Contact.htm
Mike is the man to talk to and he is realy good at getting snapped off bolts out without damaging anything if he isnt to far from you in chicago