Anyone good with stuck bolts?

I rented a balancer installation tool the other day from the Auto Parts store. There are two parts to it. One big threaded rod that holds the plate installing the balancer, and a smaller threaded rod which gets threaded into the nose of the crankshaft to keep it centered. After reinstalling the balancer I can't get the two pieces to come back apart (they thread into each other). On one end I can put a 5/8" socket -- so thats not the problem. But on the smaller piece there is just a slot in the end for a screwdriver. I have a screwdriver that fits it but I cant get it to budge.

So far I've tried boiling it, leaving it in ice for an hour, and even heating the small end with a torch and nothing seems to be working. Anyone know any tricks?

Here's some pics of what the assembly looks like.

http://www.wowway.com/~kevinrush1/POS.JPG

http://www.wowway.com/~kevinrush1/POS2.JPG

Yeah, the main problem is trying to keep the end with the slot in it from spinning. Can't seem to budge it just using a screwdriver.

thanks for the help, but I just took it back to them and they sent it back to the manufacturer as a defective part. Best part about rented tools