What kind of car do you have?
You're going to have to replace two lug studs and possibly the lug nuts. Shouldn't set you back more than five bucks if you can handle it yourself.
you stripped it. unless you want to cut off the bolt head and possibly drill out the bolt and retap the hole (if you can even safely do that with your car, i'm not sure) you should seek the assistance of a trained mechanic.
He shouldn't have to do that if he has a newer car. Most of the newer ones I've worked on unthreaded holes for the lug studs. It's just a matter of hammering the old one out once you get the bolt off and popping a new one in - build up a cylinder with washers over the stud, put the lug nut on top, and crank down until the lug stud pops into the hole.
EDIT - how many nut holes in your wheels? If you've got five, you shouldn't have a big problem driving with three for a short period of time (ie, drive it to the mechanic.)