So just what is the cause of those infamous frozen calipers anyway?

[sonerick]

Correct, there are three castings. Easiest way to find out is to look at your current calipers, it should be stamped on the side (13WH, 13WL or 13WG). Here's a little more info: http://www.toyota-4runner.org/general-discussions/66299-13wh-vs-13wg-calipers-question.html

As far as replacing the front calipers go, there is a walk-through stickied on the site: http://www.toyota-4runner.org/maintenance-detailing/63934-my-4th-gen-front-brakes-walkthrough.html