Installing an Ignition Lock Cylinder Switch in a 92 D21 Nissan Pickup.. How do I?

I have a 92 nissan truck that I got for very very cheap, it runs good and everything, but the key is broke off in the switch, and you crank it with a flat head screwdriver. Well, someone got in it and "locked" it all the way back (manual ) to where you could take the key out, and now it won't crank because you need to rest of the key I guess to turn the switch back. Can someone tell me how to install a ignition switch on it, or another way to fix the problem?? Is there any way to take the switch apart and take the tumblers out of it?? Any help would be greatly appreciated!!! Thanks in advance.