DURING THE ILS APCH TO RWY 24 (6400 FT LONG), VISUAL CONTACT WITH THE RWY WAS ESTABLISHED AT APRX 500 FT AGL AND THE ACFT WAS INDICATING 'ONE DOT' HIGH ON THE GLIDE SLOPE. WITNESSES STATED THE ACFT TOUCHED DOWN PAST THE HALFWAY POINT ON THE RWY WITH FULL FLAPS IN MODERATE RAIN. A 5 KT TAILWIND WAS PRESENT AT THE TIME AND THE RWY CONTAINED A .8% DOWNSLOPE. UPON APPLICATION OF THE BRAKES, THE PLT FOUND THEM INEFFECTIVE AND CALLED FOR FLAPS UP. BRAKING WAS STILL INEFFECTIVE AND THE PLT ELECTED TO GROUND LOOP THE ACFT TO STOP. LEFT TURNING SKID MARKS WERE FOUND STARTING 300 FEET BEFORE THE END OF THE RWY. THEY CONTINUED 120 FT BEYOND THE RWY UNTIL THE ACFT TRAVELED OFF AN EMBANKMENT. APRX3 INCHES OF WATER WAS PRESENT ON THE RWY WHEN THE ACCIDENT OCCURRED. THE ACFT TRAVELED 120 FT BEYOND THE EMBANKMENT AND COLLIDED WITH UPSLOPING TERRAIN ON THE OTHER SIDE.