In addition to mrpeter's excellent advice, sometimes the squeaking is caused by the floor boards or the subfloor having loose nails and the boards sliding up and down the slightly loose nails is the source of the squeak. In those cases, try sprinkling a fair amount of common talcum powder on the floor and sweeping it back and forth before vacuuming up the surplus. The talc has a lubricating value and it's fine enough to get into the areas that may be causing the squeak. Sometimes this works and sometimes it doesn't, but at any rate you'll have the nicest smelling floor in the neighborhood... Best of luck...