It is most likely to be just your resistor pack if your motor only runs on full speed, this is quite easy to replace but will require the removal of the heater motor this is just 3 screws (6mm socket size) and the motor will come out (with a bit of wiggling) then remove the philps screw in the end of the housing and lift the motor out and the resistor pack is just there, if the motor has stopped working all together it could be the motor thats failed, same proceedure as above just a hell of a lot more money.
Tim
February 2007