THE NONINSTRUMENT RATED PLT CALLED FLT SERVICE A DAY BEFORE THE ACCIDENT AND REQUESTED AND RECEIVED AN IFR BRIEFING FOR THE ACCIDENT FLIGHT. THE WX BRIEFER PROVIDED THE PLT WITH THE BRIEFING WHICH CONSISTED OF IFR CONDITIONS AT THE DESTINATION AIRPORT AREA WHICH INCLUDED THE ACCIDENT SITE. GND WITNESSES OBSERVED THE AIRPLANE MANEUVERING IN THE ACCIDENT AREA BEFORE IT ENTERED INTO THE 500 FT CEILING STRATUS CLOUDS. THE PREVAILING VISIBILITY WAS LESS THAN 1 MILE. THE ENGINE SOUND INCREASED RAPIDLY WHEN THE AIRPLANE ENTERED THE CLOUDS ABT 2 SECONDS BEFORE IT COLLIDED WITH THE SIDE OF THE HILL. THE ACFT EXAMINATION DISCLOSED THAT IT STRUCK THE HILLSIDE IN A LEVEL FLT ATTITUDE; THE PROPELLER BLADES AND HUB ASSY SHOWED DAMAGE CHARACTERISTICS CONSISTENT WITH HIGH POWER BEING DEVELOPED AT IMPACT. NO PREEXISTING MALFUNCTIONS AND/OR FAILURES WERE NOTED.