B737 CREW INBOUND TO TPA MISSED A TURN ON THE STAR TO THE ARPT.

Narrative

IT WAS A BEAUTIFUL EARLY EVENING WITH EXCELLENT VISIBILITY. I HAD JUST CHKED IN WITH OUR SECOND APCH CTLR WHILE THE FO WAS FLYING THE APCH. FLYING INBOUND FROM THE N ON THE PIE 039 DEG RADIAL; I SAW THE ARPT FROM SEVERAL MI AWAY. FROM THE ANGLE WE WERE APCHING THE ARPT; I HAD IT IN MY MIND THAT WE WOULD LAND ON RWY 36L WITH A L DOWNWIND; AS I HAD DONE SEVERAL TIMES BEFORE. I SAW AN ACFT APPROX 5 MI AHEAD IN A CLB AND ABOUT TO PASS THROUGH OUR ALT. WE WATCHED THIS ACFT CLB THROUGH OUR ALT AT APPROX 3 MI BUT SAW NO NEED FOR ANY EVASIVE ACTION. THIS OTHER ACFT WAS AT LEAST 3 MI AND 1000 FT VERT SEPARATION (ABOVE US) WHEN APCH CTL ORDERED AN IMMEDIATE CLB. WE COMPLIED WITH A GRADUAL CLB WHILE LOOKING FOR ANOTHER ACFT TO WHICH I THOUGHT ATC MIGHT BE REFERRING. AT APPROX 5200 FT; I TOLD ATC THAT THE OTHER ACFT WAS WELL ABOVE US AND CLBING. NO TCASII RA'S WERE EVER RECEIVED BY US. WE RETURNED TO 5000 FT AND COMPLIED WITH APCH CTL'S RADAR VECTORS FOR A L DOWNWIND TO AN UNEVENTFUL LNDG ON RWY 36L. THIS POSSIBLE LOSS OF SEPARATION AROSE WHEN WE APPARENTLY MISSED THE TURN ON THE STAR AT TUMPY INTXN. CONTRIBUTING TO THIS WAS THAT IT WAS A VERY CLR DAY AND I WAS LOOKING AT THE ARPT. AS THE INTXN PASSED BEHIND US I WAS CONVINCED THAT WE WOULD BE VECTORED FOR A L DOWNWIND. AN ADDITIONAL CONTRIBUTING FACTOR MAY HAVE BEEN THAT THIS ACFT IS A B737-200 WHICH HAS NO LNAV CAPABILITY. SINCE THE VAST MAJORITY OF OUR FLEET ARE B737-300'S; -500'S; AND -700'S; ALL OF WHICH HAVE LNAV; THERE MAY BE A RELIANCE ON THE LNAV BY SOME PLTS TO ALLOW THE AUTOPLT TO TURN THE ACFT AT THE APPROPRIATE FIXES.