OK, I'm going from memory here so I'll try my best.
Take the nut for the steering linkage and screw it on to the stud in the idler arm so that the threads are protected. Take two large hammers to the problem.
Place one hammer against the back side of the idler arm and use the other to hit the front side directly opposite. A couple of good smacks will free the stud from the tapered hole in the idler arm.
Remove the nut and now you can remove the old idler arm from the steering linkage. What ever you do, do not hit down on the end of the stud. This will bugger the threads as well as destroy the ball joint of that steering joint.
Clear as mud? Good, now go find some hammers!!