1. A surgical guidance system, comprising: a probe; a video camera affixed to the probe; trackable objects affixed to a patient and the probe; a tracking device which determines the positions of the probe and the trackable objects; a data processor with pre-stored three dimensional patient image data; and a display; wherein the data processor augments real time images from the video camera with virtual objects generated form the three dimensional patient image data in response to input from the tracking device and displays a composite image on the display.