AN MD80 ON APCH TO RDU WAS GIVEN RVR BELOW MINIMUMS; BUT THEY HAD THE RWY IN SIGHT SO THEY LANDED.

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ON THE BUZZY 6 ARR INTO RDU. THE CURRENT ATIS WAS 1 SM VISIBILITY; 400 FT OVCST. WE BRIEFED THE ILS RWY 23R FOR LNDG. XING THE BUZZY INTXN (37 DME FROM RDU) WE COULD SEE THE ARPT AND RWY LIGHTS. DURING THE FLT; I HAD RECEIVED MULTIPLE ATIS'S; EACH ONE SHOWED IMPROVEMENT IN VISIBILITY AND CEILING. XING BUZZY; IT MADE SENSE THAT THE ARPT HAD IMPROVED MORE FROM THE RPT ON THE CURRENT ATIS. APPROX 10 MI OUT; APCH TURNED US DOWNWIND FOR RWY 23R. THE RWY WAS IN SIGHT AT ALL TIMES. APPROX 9 DME APCH GAVE ME A BASE TURN AND TOLD ME TO DSND TO 2200 FT. WHEN LEVELING OFF AT 2200 FT; APCH GAVE ME A HDG FOR BODLY (FAF) AND TOLD ME TO JOIN THE LOC FROM THAT HDG. I WAS VERY CLOSE TO BODLY AT THIS TIME. APCH ADVISED US WE COULD NOT EXECUTE A CAT II APCH DUE SOME EQUIP ON THE FIELD (LACK THEREOF). WE ADVISED THEM WE HAD THE RWY IN SIGHT. APCH SAID TO CONTACT THE TWR. WE CALLED TWR AND TOLD THEM WE HAD THE RWY IN SIGHT. TWR CLRED US TO LAND. WE HAD THE RWY IN SIGHT WITH NORMAL MANEUVERS FOR LNDG THROUGHOUT THE ENTIRE PROCESS. I DO NOT KNOW EXACTLY WHERE THE RVR READOUTS WERE READ TO US. SOMEWHERE BTWN OUR DSCNT ON BASE AND LOC INTERCEPT. I WAS NOT THAT CONCERNED WITH THE RVR BROADCASTS BECAUSE I HAD BEEN LOOKING AT THE RWY FOR THE LAST 15-20 MINS. IT FELT LIKE APCH WAS VECTORING US FOR A VISUAL APCH. THEY WERE BRINGING US IN CLOSE TO THE ARPT FOR A TURN TO FINAL. ANOTHER ACR WAS ON APCH BEHIND US. THEY WENT AROUND. THAT IS WHEN THE CAPT AND I REALIZED WE MAY HAVE BEEN IN THE WRONG. NEXT TIME I WILL BE MORE DILIGENT TO RESEARCH REQUIRED VISIBILITY FOR AN APCH EVEN IF I CAN SEE THE RWY.