THE PLT RENTED N8912N TO TRANSPORT FIVE PASSENGERS TO COLORADO FOR A SINGING COMPETITION. THE PASSENGERS HAD NOT MADE ALTERNATE TRAVEL PLANS. THE PLT RECEIVED A WEATHER BRIEFING, WHICH INDICATED LOW CLOUD CEILINGS, MODERATE TURBULENCE AND ICING ALONG HIS PLANNED ROUTE. HE FILED 10,500 FT AS HIS CRUISING ALT. SUBSEQUENTLY, THE AIRPLANE COLLIDED WITH A 13,700 FT HIGH MOUNTAIN AT ABOUT THE 12,000 FT LEVEL. WEATHER AT THE ACCIDENT SITE WAS IFR. THE PLT WAS NOT INSTRUMENT RATED.