I think what you are refering to is a rotor. Its the thing that the brake pads rubs against to bring the car to a stop. If it is warped, you will get some wierd jerking and such. I can't say for sure if its the problem, but you can get new rotors for your car from this site, they are the cheapest I could find, I would go with some ATE, not the slotted version, just the solid ATE rotors. They might also be called disks, these are the same things.