MD88 FLT CREW HAS AN ARR CHANGE FOLLOWED BY A CLOSE-IN RWY CHANGE ON APCH TO ATL. THEY CHANGE THE INFORMATION IN THE FMS; BUT NEGLECT TO UPDATE THE NAV RADIOS AND CAPTURE THE WRONG ILS.

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ON ARR TO ATL WE WERE APCHING ODF ON THE FLCON 3 WHEN WE WERE GIVEN A VECTOR TO THE W AND TO EXPECT ROUTING VIA DIRECT PECHY AND THE PECHY 3 ARR. WE SET UP FOR THIS AND WERE CLRED TO FLY THE PECHY EXCEPT VECTORS TO DOWNWIND FOR RWY 26R. LEAVING 10000 FT WE COMPLETED THE APCH CHKLIST INCLUDING SETTING THE NAV RADIOS FOR RWY 26R. AT 6000 FT WE WERE TOLD TO CHANGE RWY TO RWY 27L FOLLOWED QUICKLY BY A DSCNT TO 4000 FT AND THEN A TURN TO THE S. THE FO WAS FLYING AND HE UPDATED THE FMS FOR RWY 27L; BUT DURING THE TURN AND DSCNT WE NEGLECTED TO CHANGE THE NAV RADIOS TO RWY 27L. WE RPTED THE ARPT IN SIGHT BUT IT WAS STILL FAIRLY HAZY. WE WERE CLRED FOR THE VISUAL TO RWY 27L AND THE FO ARMED THE ILS WHICH CAPTURED TO LOCALIZER ALMOST IMMEDIATELY. THE CTLR ASKED US IF WE WERE SURE WE WERE ON RWY 27L AND INITIALLY WE ASSURED HIM WE WERE. ALL THE RAW DATA LOOKED GOOD UNTIL I NOTICED WE WERE HEADING TOO FAR N. I TOOK THE ACFT; DISCONNECTED THE AUTOPLT AND TURNED BACK TO THE CORRECT RWY AS THE CTLR AGAIN SAID WE LOOKED TO BE ON THE WRONG ILS. WE HAD TFC 1000 FT ABOVE US; BUT THERE WAS NO CONFLICT. I TURNED THE ACFT BACK TO THE FO AND WE FLEW AN UNEVENTFUL VISUAL APCH AND LNDG TO RWY 27L. THE ERROR WAS CAUSED BY MULTIPLE APCH AND RWY CHANGES; INCLUDING AFTER THE APCH CHECKS WERE COMPLETE. ALSO TOO MUCH ATTENTION WAS PUT IN THE FMS AND NOT ENOUGH ON THE BASICS SUCH AS NAV RADIOS.SUPPLEMENTAL INFO FROM ACN 791584: I NOTED TO THE CAPT WE APPEARED TO BE CORRECTING TO THE LOC COURSE BUT WERE DRIFTING N OF THE EXTENDED RWY 27L CTRLINE. THE CAPT TOOK THE ACFT AS THE CTLR NOTED WE APPEARED TO BE INTERCEPTING THE RWY 26R LOC AND ISSUED A TFC ALERT FOR ANOTHER ACFT 1000 FT ABOVE AND LEVEL. BY THEN WE HAD CORRECTED TOWARD RWY 27L. I THEN PERFORMED THE LNDG. COCKPIT TASK LOADING CONTRIBUTED TO THIS INCIDENT. THE SEVERAL CHANGES IN ARR ROUTING; VECTORS; AND ALTITUDE AND SPEED CHANGES LED TO TASK MISPRIORITIZATION. I SHOULD HAVE IMMEDIATELY PUT THE CORRECT ILS NAV FREQUENCY IN FIRST. THE HAZY CONDITIONS COUPLED WITH OUR DISTANCE FROM THE FIELD; CAUSED THE PERCEPTION THAT OUR POSITION; HEADING; AND LOC INTERCEPT WERE; AT LEAST INITIALLY; CONSISTENT WITH THE RWY 27L APCH.