AFTER BEING CLRD FOR AN ILS RWY 13 APCH TO SCHOLES FIELD, THE ACFT CRASHED APRX 75 YDS NORTH OF THE RWY & CAME TO REST INVERTED ON A HDG OF 330 DEG. THERE WAS EXTENSIVE DAMAGE TO THE ENG & PROP, & THE FUSELAGE WAS BROKEN AFT OF THE COCKPIT, BUT THE WINGS & EMPENNAGE WERE RELATIVELY INTACT. ALTHO, BOTH OCCUPANTS SURVIVED THE ACDNT, THE PLT WAS UNABLE TO REMEMBER THE OCCURRENCE DUE TO HIS INJURIES. AN INVESTIGATION REVEALED THE WX HAD BEEN VARIALBLE. AT 0656 CST, WHEN THE PLT 1ST CTCD HOUSTON APCH CTL, THE GALVESTON WX WAS IN PART: INDEFINITE CEILING, 100' OBSCD, VIS 3/16 MI WITH FOG. AT 0718, THE PLT WAS ADZD OF NEW WX WHICH WAS IN PART: SKY PARTIALLY OBSCD, 300' THIN SCATTERED, CEILING 800' OVC, VIS 3/4 MI WITH FOG. AT 0736, THE PLT WAS ADZD OF A SPCL WX OBS, WHICH WAS IN PART: SKY PARTIALLY OBSCD, 300' THIN SCATTERED, 800' OVC, VIS 3/16 MI WITH FOG. A SUBSEQUENT WX OBS (NOT AVAIL TO PLT WHEN HE WAS CLRD FOR THE APCH AT 0742) WAS IN PART: 300' OBSCD, VIS 1/16 MI WITH FOG. WX MINS FOR THE ILS APCH WERE: 200' CEILING & 1/2 MI VIS.