Lower COntrol Arm Problem

I bought yet again another Honda, this time a 1997 Honda Civic LX. One of the front control arms is bent. I have a new one and everything is off of the old one except for the castle nut that hold the radius arm on. I try to loosen it the whole thing spins, the ball joint I believe? But anyways how can I get this off easily? I just want the castle nut off with out having to dissasemble anything else??? This is really making me mad. When I got the new control arm I cut this bolt off of the car I got it from in the junk yard. HELP ME PLEASE!

You mean the lower ball joint?

first choice - impact
second choice - grab the ball joint with channel locks on the rubber boot, it's rec. to replace the ball joint at this point.