ok, is this screw located on the case, or somewhere else, like on a hard drive etc. etc.
if its on the case, your best bet is to get a drill/drill bit thats id say 1/8" less in diameter than the screw and just drill it out. Then just use some compressed air to blow the particles out of the case, pay special attention to sockets and slots as metal particles inside those can be disasterous. Oh, when you are doing this, be sure to remove your in-case speaker as it is magnetic and will attract all steel particles.