THE PILOT HAD OBTAINED 3 WEATHER BRIEFINGS BEFORE THE NIGHT FLIGHT. FORECAST WEATHER WAS IMC ENROUTE AND AT DESTINATION, DETERIORATING THROUGH MIDNIGHT. THE PILOT FILED VFR TO SAGINAW AND IFR TO HIS DESTINATION. HE WAS NOT INSTRUMENT-RATED. THE PILOT BROKE OUT BENEATH A 600-FT OVERCAST AND ATTEMPTED FOR THE NEXT HOUR TO LAND. THE AIRPLANE EVENTUALLY FLEW INTO TREES ON AN EXTENDED DOWNWIND IN THE LANDING CONFIGURATION.