THE F/O WAS AT THE CONTROLS FOR THE ILS APCH TO SLC. FOG SEEDING WAS IN PROGRESS, PRODUCING VARIABLE VISIBILITIES. THE APCH COMMENCED WITH RVR WELL ABOVE CAT I MINS. AT DECISION HEIGHT(DH), THE CAPT CALLED 'LIGHTS IN SITE'. THE F/O CONTINUED THE APCH DESCENT THRU DH. THE ACFT THEN REENTERED IMC AND THE CAPT CALLED FOR MISSED APCH. THE F/O ADDED PWR AND ESTABLISHED A WINGS LEVEL, 10 DEG NOSE-UP ATTITUDE ON THE GYRO HORIZON AS THE CAPT EXECUTED CHECK LIST ITEMS. THE CAPT THEN NOTED THE ACFT WAS HEADING 20 DEGS RIGHT OF COURSE AND THE RIGHT WING DOWN ATTITUDE ON HIS GYRO HORIZON AT WHICH TIME HE CALLED 'TURN LEFT AND PULL UP.' THE ACFT LEFT MAIN LANDING GEAR CONTACTED A 45 FT HIGH ILS ANTENNA STACK 1049 FT DOWN THE RWY, 400 FT RIGHT OF CENTERLINE. THIS SEPARATED THE LEFT MAIN GEAR. THE ACFT DIVERETED TO PIH WHERE ADDITIONAL DAMAGE WAS SUSTAINED DURING LANDING. TESTS SHOWED THE F/O GRYO HORIZON HAD BAD BEARINGS AND THE 'OFF' FLAG WAS INOP. THE F/O'S ALTIMETER ALSO READ 100 FT HIGH.