there is a device called an "easy out" or a "retractor" and it is a drill bit that is threaded backwards so when you drill down the middle of the screw the screw will come right out.... or if the screws are easily accessible then use a dremel saw and cut a slit along the screw head and then use a flat screw driver to get it out... heres a link to a screw extractor [link]http://www.cvfsupplycompany.com/5pcscrewexse.html[/link]