Impact driver
This one is a Craftsman bought at sears for ~ $25. They do have a cheaper model in a case, but its mail order only. This one they actually stock at the store.
What you do is use the phillips head and bang it with a hammer hard on the flat end while turning the impact driver to loosen the screw.
Here is the special rear caliper tool:
Also available at sears for ~ $12. It looks weird, but each side is made for a different caliper setup. Find the correct one to use and with a 3/8" rachet, you can now turn the rear caliper piston to its retracted position.