BEFORE TAKING OFF FROM JACKSON, MS, THE PILOT RECEIVED A WEATHER BRIEFING BY RADIO AND FILED AN IFR FLIGHT PLAN TO MCCOMB, MS. DURING ARRIVAL AT MCCOMB, THE WEATHER WAS IFR WITH AN INDEFINITELY OBSCURED CEILING AT ZERO FT, VISIBILITY 1/2 MILE IN FOG, WIND 160 DEGREES AT 7 KNOTS. DURING AN ILS LOCALIZER APPROACH, THE AIRCRAFT MADE CONTACT WITH TREES ABOUT 2900 FT FROM THE APPROACH END OF THE RUNWAY. THE TREES WERE ABOUT 50 TO 60 FT TALL AND THE GROUND LEVEL WAS APPROXIMATELY 400 FT MSL. THE MINIMUM DESCENT ALTITUDE (MDA) FOR THE APPROACH WAS 800 FT MSL. THE INITIAL IMPACT POINT WAS ALONG THE CENTERLINE OF THE APPROACH TO RUNWAY 15. AFTER THE INITIAL IMPACT, THE AIRCRAFT FLEW ABOUT 630 FT AND THEN CRASHED IN A WOODED AREA ABOUT 400 FT LEFT OF THE CENTERLINE OF THE APPROACH. AN INVESTIGATION REVEALED NO INDICATION OF A MALFUNCTION OR FAILURE OF THE ENGINES.