That could be a number of problems.. My first guess is your rotor's are warped, so when you hit the brakes it cause the car to shake. If your pads are done then your brake sensor would come on inside the car(that's if it is hooked up and the fuse and bulb work).
If not then it could be other things, ball joints etc.. loose lugnuts.
1994 318is-Sold July 13th 2010.. Sad Sad Day