DURING A LOW VISIBILITY APCH; ACFT CONFIGN IS NOT CORRECT AND NOT NOTICED UNTIL GPWS ACTIVATES WARNINGS.

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ENRTE WE BRIEFED AND SET UP FOR A CAT IIIA FOR RWY 27 IN IAH. FO FLYING; CAPT MONITORING AND LNDG ACFT. APCH WAS TOLD OF A CAT IIIA APCH. WE WERE VECTORED TO ILS RWY 27; R-HAND DOWNWIND. PRIOR FINAL APCH FIX; WE WERE TOLD TO GET TO TWR. NO RESPONSE FROM TWR. AFTER SEVERAL CALLS WE WERE CLRED TO LAND RWY 27. DURING THIS TIME I CALLED '1000 FT.' COMING BACK INTO THE LOOP; I CALLED THE 500 FT; 400 FT; 300 FT; AND 200 FT CALLS. NEXT CALL WOULD HAVE BEEN 'I HAVE THE ACFT' AT 150 FT AGL. JUST PRIOR TO THAT; WE GOT THE GPWS ALARM 'PULL UP.' I SAW GEAR/FLAPS ON ADI. I CALLED FOR A GAR IMMEDIATELY. FO EXECUTED IT. AT THAT TIME I BELIEVE THE FLAPS WERE STILL AT 15 DEGS. MISSED APCH WAS EXECUTED TO 3000 FT. RADAR VECTORS TO ANOTHER APCH. ATC ASKED ABOUT GA. WE TOLD HIM THAT WE DID NOT MEET OUR PARAMETERS. ANALYSIS: 1) AS A CAPT; I GOT INVOLVED WITH ATC AND FAILED TO MONITOR PROGRESS OF FLT. 2) FO NEGLECTED TO FLY ACFT AS HIS PRIMARY DUTY; TRYING TO HELP ME. I WAS DISTR BY THAT BUT COULD NOT REALIZE WHAT WAS HAPPENING. 3) FO WAS AT TIMES TRYING TO 'RUN ACFT.' I LET IT GO; TRYING TO BE A NICE GUY. MAYBE HE WAS JUST TRYING TO BE HELPFUL. I HAD A TALK WITH HIM ABOUT IT AFTER THIS INCIDENT. I WILL KEEP A BETTER EYE ON COCKPIT DISCIPLINE. 4) IT WAS AN ALL-NIGHTER; SO FATIGUE WAS PROBABLY A SLIGHT FACTOR. 5) THE WX WAS GETTING WORSE BY THE MIN. ON APCH GREATER THAN 6000 FT RVR TO RVR APPROX 2000 FT FOR SECOND APCH; CEILING DOWN TO 100 FT. 6) ATC CAUSED DISTRS AT A CRITICAL FLT PHASE; DUE TO NOT ATTENDING RADIO FREQ. I NORMALLY CHK FOR FLAPS AND SPD BRAKES AT 1000 FT/500 FT. BY MAKING ALL THE REQUIRED CALLOUTS EVERYTHING SEEMED ALRIGHT. FO WAS WAY TOO PASSIVE; NEVER CALLED FOR FLAPS AND COMPLETION OF LNDG CHKLIST.