DURING THE TAKEOFF ROLL ON RWY 13 THE AIRCRAFT BEGAN TO DRIFT LEFT. THE PILOT WAS UNSUCCESSFUL IN CORRECTING FOR THE DRIFT AND THE AIRCRAFT IMPACTED A SNOWBANK ALONG THE EAST OUTBOARD EDGE OF THE RUNWAY BEFORE NOSING OVER. SUBSEQUENT EXAMINATION OF THE AIRCRAFT REVEALED NO MECHANICAL MALFUNCTION WITH EITHER THE BRAKES, RUDDER SYSTEM OR NOSEWHEEL STEERING AND THE PASSENGER SEATED IN THE FRONT RIGHT COCKPIT SEAT REPORTED THAT HE DID NOT HAVE HIS FEET ON THE RUDDER PEDALS. WINDS WERE NORTHWESTERLY AT 5 KNOTS.