Hi John,  What you need is known as an 'easy-out'.  Basically, it's a
backwards (left handed) carbon steel screw.  Most automobile parts
stores have them but the one you need has to be very small.

Then you have to drill a small hole right in the center of the broken
screw, down about 1/4 inch (1 cm.).  Then put the easy-out into a
tee-bar (vise-grips will work in a pinch) and twist it in counter-
clockwise.  As it screws into the hole, it's bite on the broken screw
will get tighter and tighter until the broken screw starts backing
out.  I've had tremendous luck with easy-outs and use them anytime a
screw gets broken.  In fact, I used one just last week.

Musically,

John Tuttle         "Self-Playing Pianos" http://www.PlayerCare.com
407 19th Avenue           E-Mail: JohnTuttle@PlayerCare.com
Bricktown, NJ 08724         "We Keep Your Music Rolling"