Creaking floors due to construction project

We moved into a ranch style home October 2007, started having the basement finished January 2008. Noticed that everywhere contractor put up a wall in basement the main level of the floors began to creak. What can be done to stop the creaking and prevent any future creaking problems?

The squeaking will come from between the boards, between layers, or at the joists. Depending on the construction of the floor, you can screw down the subfloor to the floorboards and into the joists. If surfaced with hardwood you can screw from underneath into the hardwood. Measure the floor thickness and purchase screws at least 1/4inch shorter. Longer screws can be angled into the floor through the joists.