Just to clarify, do you get the same squeaking sound when pressing the brake pedal while the car is stationary? If so, it's probably a bushing, loose bolt, or something in the pedal linkage.
If it does not squeak when the car is stopped and only when it is in motion, then another possibility is that the squeak is in the front suspension....which dives whenever the brakes are applied. With the car stopped, you could try bouncing the front end and see if you hear anything. I would recommend you lift the hood and press down on the body of the car, rather than pressing down on either the hood or bumper.
Either way, a trip to the dealership might be your best bet. Good luck tracking it down.