If the screw is in tight or if you can wedge it, try a tool called an
"Easy Out".  You drill a small hole in the center of the screw and
insert this tool, which has a left hand thread, into the hole.  The tool
cuts a rough thread into the screw as you tighten it in, by turning it
counter-clockwise, and eventually it should remove the screw.

Good luck.

Ed Kigler