THE TWO NON INSTRUMENT RATED PILOTS (OWNER/PILOT IN COMMAND AND SECOND PILOT) AS WELL AS A PASSENGER DEPARTED MEDICINE HAT, ALBERTA, CANADA, ON A PLEASURE FLIGHT TO LAS VEGAS, NEVADA. UPON ARRIVAL AT GREAT FALLS, MONTANA, BOTH PILOTS WERE BRIEFED ON THE INTENDED ROUTE OF FLIGHT VIA POCATELLO, IDAHO, AND VFR FLIGHT WAS NOT RECOMMENDED. THE BRIEFER SUGGESTED AN ALTERNATE ROUTING VIA WYOMING. THE OWNER/PILOT IN COMMAND OVERRODE THE SECOND PILOT'S ACCEPTANCE OF THE ALTERNATE ROUTING AND THE AIRCRAFT DEPARTED. APPROACHING POCATELLO ONE OF THE PILOTS RADIOED THAT WEATHER CONDITIONS WERE 'CLOSING IN' ON THE FLIGHT AND A WITNESS IN THE VICINITY OF THE CRASH SITE REPORTED LOW CEILINGS/CLOUDS, FOG, LIGHT SNOW AND REDUCED VISIBILITIES DURING THE LATE MORNING/EARLY AFTERNOON OF THE ACCIDENT. THE AIRCRAFT IMPACTED FROZEN GROUND IN A STEEP NOSE LOW ATTITUDE WITHOUT CRACKING. BREAKING THE ENGINE CRANKCASE AFTER STALLING AT LOW ALT.