CARGO FLC SETS WRONG XING RESTRICTION IN FMC. MISSES XING RESTRICTION.

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ATC ISSUED A XING RESTRICTION TO DSND TO FL290 50 MI SW OF BNA ON J42. THE CAPT WHO WAS ALSO FLYING THE ACFT AT THE TIME (ON AUTOPLT) ENTERED THE XING RESTRICTION INTO THE FMC AS 5 MI SW. I; THE FO WAS HANDLING THE RADIOS AND READ THE XING RESTRICTION BACK TO ATC CORRECTLY; THE CAPT HOWEVER MISINTERPRETED THE RESTRICTION AND ENTERED IT AS SUCH. AT EXACTLY 50 SW OF BNA MEMPHIS CALLED AND ASKED US WHAT OUR XING RESTRICTION WAS; AND WHAT OUR DME FROM BNA WAS. THERE WAS NO CONFLICT WITH OTHER TFC AND WE WERE CLRED TO DSND TO 270. COMPANY TECHNIQUE IS FOR THE PNF TO ENTER THE INFO INTO THE FMC; IT IS NOT UNCOMMON HOWEVER; FOR THE PF TO DO THE FMC WORK; ESPECIALLY IN THE ENRTE PHASES OF FLT WHEN THE AUTOPLT IS FLYING THE AIRPLANE AND THE WORKLOAD OF THE PNF IS SOMETIMES HIGHER WHEN WORKING THE RADIOS; TALKING TO COMPANY; AND GETTING THE ATIS. MY ERROR WAS IN NOT CHKING THE CAPT'S INPUT INTO THE FMC AS IS COMPANY TECHNIQUE. A CONTRIBUTING FACTOR TO THIS ERROR WAS THE CREW'S LACK OF ALERTNESS DUE TO A COMPANY RESCHEDULE. INSTEAD OF A 4 HR LAYOVER EARLIER THAT MORNING IN JACKSON; MS; WE WERE REDISPATCHED TO DFW TO RESCUE A BROKEN COMPANY ACFT. THIS MEANT WE DID NOT GET OUR USUAL 3 1/2 HR NAP AND WE WERE QUITE TIRED. IN THE FUTURE I WILL CHK ALL OF THE OTHER PLT'S INPUTS INTO THE FMC AND ASK HIM TO DO THE SAME FOR ME.