B757 FLC ALIGNS WITH THE WRONG RWY ON VISUAL APCH. FOLLOWING WRONG ACFT CALLED AS TFC.

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DURING A BUSY AND EXPEDITED BOIDS 5 ARR; WE WERE ASSIGNED 250 KTS; GIVEN SOUTHERLY HDG PASSING PIVIT; DSND TO 5000 FT; KEEP UP SPD; LEVEL AT 6000 FT; DSND TO 5000 FT; TURN 080 DEGS; COMMUTER TFC. DO YOU SEE THE TFC? NO. DO YOU SEE THE ARPT? YES; RWY 18L IN SIGHT. CLRED RWY 18L VISUAL. CAPT WAS PNF. PF RPTED TFC IN SIGHT. PNF HAD HEAD DOWN DUE TO COMMUTER TFC ON TCASII LESS THAN 3 MI; TUNING AND IDENTING RWY 18L LOC; CHANGING TO 124.15; ETC. HAD HAZE AND LOW SCUD; BUT VFR. TWR CALLED TO ADVISE THAT WE WERE ALIGNED WITH RWY 17C. WHEN I LOOKED OUT I CONCURRED AND WE MADE AN IMMEDIATE CORRECTION. OTHER THAN EMBARRASSMENT I DO NOT THINK THERE WAS ANY CONFLICT OR OTHER PROB. THIS SHOULD NOT HAVE HAPPENED; BUT WE FAILED TO PROTECT OURSELVES FROM ENTRAPMENT BY APCH IN A TIMELY MANNER. I WAS TUNING AND IDENTING RWY 18L ILS FOR RAW DATA BUT HAD NOT DONE IT SOONER BECAUSE OF BEING BUSY COMPLYING WITH APCH INSTRUCTIONS AND HALF EXPECTING TO GO TO THE E SIDE BECAUSE OF THE WAY WE WERE BEING EXPEDITED. THE CLOSE TFC ON TCASII WAS A CONCERN. MEANWHILE THE PF CALLED OUT THE TFC; WHICH TURNED OUT TO BE THE WRONG TFC GOING TO RWY 35R; AND BEGAN HIS ALIGNMENT TO RWY 17C FROM A HIGH APCH WHEN THE TWR CALLED US. THIS COULD HAVE BEEN AVOIDED IF THE PNF HAD HAD HIS HEAD UP MORE AND IF THE PF WAS AS DISTRUSTFUL OF RELYING ON A VISUAL ON SPOTTED TFC FROM AN ANGLED INTERCEPT TO FINAL AS THE PNF IS. ALSO IF THE PF HAD USED RAW DATA OR ARMED LOC HE WOULD HAVE CAUGHT THE ERROR. THE FREQ WAS TUNED; ALTHOUGH NOT IDENTED EARLY.