Originally posted by KellyJoe:
This might sound crazy but it really works. That is if the head of the screw isn't totally worn out. Get the largest bit screwdriver that will fit into the screw, wet the end of it (screwdriver) with water or whatever you might have handy, stick tip into small jar of baby powder, flour, fine dirt, etc. You now have a screwdriver covered in powder which acts to grip the screw and aid in backing it out. Honest it works. Old Army helicopter maintenance trick.
Good luck!