THE PLT RECEIVED 2 WX BRIEFINGS, ONE ON THE EVENING BFR THE FLT, ANOTHER AT 1009 EST, WITHIN 3 HRS OF THE TKOF TIME. IFR CONDITIONS WERE FORCASTED AT THE UNCONTROLLED, DESTINATION ARPT. THE PLT FILED AN IFR FLT PLAN, BUT DID NOT LIST AN ALTERNATE ARPT. THE ACFT DEPARTED BOCA ROTON, FL AT 1257 EST. THE FLT WAS UNEVENTFUL EN ROUTE & ALL COMMUNICATIONS WERE NORMAL. DURING ARRIVAL, THE PLT WAS CLEARED FOR A VOR 3 APCH TO RWY 16. THE MIN DSCNT ALT (MDA) FOR THE APCH WAS 800 FT MSL (595 FT AGL) AND THE MIN VIS WAS 1 MI. SVRL WITNESSES AT & NEAR THE ARPT SAW OR HEARD THE ACFT. THEY DESCRIBED THE ACFT AS CROSSING THE ARPT FROM THE WEST SIDE TO THE EAST. THOSE WHO SAW IT DESCRIBED IT TO BE APRX 150 TO 200 FT AGL, IN & OUT OF THE CLDS. REPORTEDLY, THE ACFT THEN CIRCLED & CROSSED THE ARPT AGAIN. SUBSEQUENTLY, IT STRUCK AN 80 FT TREE, THEN IMPACTED THE GND IN A STEEP DESCENT. THERE WAS NO EVIDENCE OF FAILURE OF MALFUNCTION OF THE AIRFRAME OR PWRPLNT BFR IMPACT. THE ACFT WAS ESTIMATED TO BE 46 LBS OVR THE MAX GROSS WT LMT DURING IMPACT.