Like Fatparrot said, they are called Easy Outs. First you have to drill a hole into the screw head so you can fit the easy out in there. The easy out is nothing more than a coarse, reverse threaded screw. They do work well if you know how to use them. If you are unfamiliar with them, I suggest you practice on a screw first, and then attempt the project at hand.
Busted Phillips Screws
one of the lugs on my speakers came loose , so I used a power screw driver to remove the Phillips screws holding the plate in the back. 3 out of the six screws came out fine. The other three had the indentaions smashed, now I am stuck with three phillips screws that I can get out. Will seek the advice of someone more mechanically inclined then myself, but any advice is appreciated. My thought is to take a drill and destroy the screws completely. However I wont do anything until I consult with a few friends. THX