DRG ARRIVAL, THE CREW OF US AIR FLT 499 LNDD ON RWY 24, WHICH WAS CVRD WITH SNW. RPRTDLY, WHILE LNDG, THE ACFT TOUCHED DWN APRX 1800 TO 2000' BYND THE DISPLACED THRESHOLD. ALTHO ARMED, THE SPOILERS DID NOT AUTO-DEPLOY, SO THE CAPT OPERATEDTHEM MANUALLY. HE LOWERED THE ACFT'S NOSE, ACTUATED REVERSE THRUST & APPLIED BRAKES. THE BRAKES WERE NOT EFFECTIVE. SUBSEQUENTLY, THE ACFT CONTD OFF THE END OF THE RWY, RAN OVR A RWY END ID LGT, STRUCK A FENCE & CAME TO REST STRADDLING A ROAD. THE CREW HAD PLANNED ON MAKING AN ILS APCH TO RWY 6, BUT THE RVR WAS ONLY 2800' & A MIN RVR OF 4000' WAS REQD FOR THAT RWY. THE CREW ELECTED TO LND ON RWY 24, SINCE 1/2 MI VIS WAS SUFFICIENT FOR THAT RWY. HOWEVER, THE APCH WAS MADE WITH A QTRG TAIL WND & APRX 10 KTS ABV VREF. TAIL WND LNDGS WERE NOT AUTHORIZED ON RWY 24 IN WET/SLIPPERY CONDS. THE RWY BRAKING ACTION WAS RPRTD AS FAIR-TO-POOR. THE PLT'S HANDBOOK CAUTIONED THE CREW TO MONITOR THE SPOILERS WHEN LNDG ON SLIPPERY RWYS, SINCE THE SPOILERS AUTO-DEPLOY ONLY WITH WHEEL SPIN-UP OR WHEN THE NOSE WHEEL IS ON THE GROUND.