...what's going on with my brakes?...?

so, here's the problem, sometimes when I am coming to a stop and put on the brakes, the car will stop once, then kinda squeek and lurch forward and skid a foot or so before coming to the 'real' and final stop...this only happens sometimes but it's not good when I'm at a stop sign or pulling out to turn and it lurches forward like that...what's going on? thanks for your help!!~