FO MISSED PROGRAMMED FMC OF A B737-500 DURING DSCNT CAUSING AN UNDERSHOOTING XING ALT.

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OUR CLRNC WAS TO CROSS QUAIL INTXN AT 17000 FT AT 250 KTS. FO WAS FLYING; AND HAD PROGRAMMED THE FMC TO CROSS QUAIL INTXN AS INSTRUCTED. HOWEVER; WHEN HE PUT IT ON THE LEGS PAGE; HE PUT IT IN BACKWARDS; THAT IS; FL250 AT 170 KTS. THE FMC SHOWED IT AS 170/250. AT FIRST GLANCE IT LOOKED OK; BUT WE SOON REALIZED THE ACFT WASN'T STARTING DOWN WHEN WE EXPECTED; AND WAS GOING TO BE CLOSE AT QUAIL INTXN. AS WE APCHED THE INTXN AND IT BECAME OBVIOUS THAT WE WEREN'T GOING TO QUITE MAKE IT; ZDV HANDED US OFF TO DEN APCH AND I ADVISED THEM THAT WE WERE GOING TO BE A BIT LATE AT QUAIL INTXN. THEY MADE NO REMARK TO THIS AND CLRED US TO 13000 FT. WE MISSED QUAIL BY ABOUT 1000 FT AND 30 KTS. WE SLOWED TO 250 KTS AND CONTINUED TO 13000 FT. NO KNOWN CONFLICTS WERE CREATED. A BACK-UP DSCNT POINT ARRIVED AT WITH ANOTHER METHOD IS THE NORM; HOWEVER; WE GOT BUSY AND NEITHER ONE OF US NOTICED THE ERROR UNTIL IT WAS TOO LATE. THE FO HAD 2 MONTHS IN TYPE. I HAVE 600 HRS IN THE 500 SERIES TYPE ACFT AND 6000 HRS IN TYPE.