ACR LINES UP WITH WRONG RWY COMPLEX.

Narrative

WE WERE ON APCH TO DFW FROM THE NE. AT ABOUT 10 MI OUT WE WERE CLRED FOR A VISUAL APCH TO RWY 17L; AS I SAID WE HAD THE ARPT IN SIGHT. THE EASTERN HALF OF THE FIELD WAS IN THE SHADOW OF A CLOUD. WE THOUGHT WE WERE LOOKING AT RWYS 17L&R BUT WERE ACTUALLY LOOKING AT RWYS 18L&R. THE BIG ACR MAINT FACILITY LOOKED LIKE THE MIDFIELD COMPLEX FROM THAT DISTANCE. WE CHANGED TO TWR FREQ AND WERE GIVEN TFC TO FOLLOW. WE COULDN'T FIND THIS TFC AS IT WAS APCHING THE RWY 17L WE WERE STILL NOT LOOKING AT. AT THIS POINT WE WERE ABOUT 5 MI OUT AND STILL DID NOT SEE RWYS 17L&R. OUR NAV WAS SET UP FOR RWY 17L. THEN TWR ASKED US IF WE WOULD LIKE RWY 17R. WE SAID WE WOULD. BEFORE HE COULD CLR US; THE RADIO WAS INTERRUPTED BY ANOTHER ACFT; SO WE STARTED DOING THE BEFORE LNDG CHKLIST. WE CONFIRMED CLRED TO LAND RWY 17R. THE FO AT THIS POINT WAS IGNORING THE INSTS BECAUSE THEY WERE NOT YET SET UP FOR THE NEW LNDG RWY. NOW WE WERE ABOUT 2/3 OF THE WAY BTWN RWY 17R AND RWY 18L WHEN WE SAW RWYS 17L&R. I TOLD TWR WE HAD OVERSHOT RWY 17R. HE CLRED US TO LAND ON RWY 18L. THE REST OF THE APCH AND LNDG WERE NORMAL.