A B737-300 CREW; DSNDING INTO LAS; UNDERSHOT PUBLISHED STAR ATC ASSIGNED ALT.

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ON THE SKEBR 1 (RNAV) STAR TO LAS; WE WERE TOLD TO CROSS THE MISEN INTXN AT FL240. WE BOTH ACKNOWLEDGED THE CLRNC AND ACKNOWLEDGED FL240 WAS LOADED IN THE 'BOX' AS THE XING RESTR ALT FOR MISEN. I FAILED TO NOTICE THAT THE ALT IN THE FMC WAS DEPICTED AS FL240A; WHICH CAUSED OUR DSCNT PROFILE TO BE BASED ON THE NEXT 'HARD' ALT IN THE BOX. I REALIZED WE WERE ABOVE PROFILE AT 2 NM PRIOR TO MISEN AND PUSHED THE NOSE OVER IN AN ATTEMPT TO MAKE THE RESTR. WE WERE AT FL260 WHEN THIS TOOK PLACE; AND I THINK WE WERE ABOUT 1000 FT ABOVE PROFILE BY THE TIME WE CROSSED MISEN. THE FO WAS 'OFF FREQ' OBTAINING ATIS FOR LAS DURING THIS EVENT. OF PARTICULAR IMPORTANCE HERE: ON THE SKEBR 1 ARR; THE MISEN INTXN IS A HARD ALT XING AT FL240. HOWEVER; THE SOFTWARE IN THE FMC LOADED IS AT FL240 OR ABOVE (FL240A). IT IS STILL MY FAULT BECAUSE I FAILED TO CATCH THE BAD INFO THAT WAS LOADED; BUT THIS SIT SETS US UP FOR VIOLATIONS/FAILURE AND SHOULD BE CORRECTED. AS WE CROSSED MISEN; ZLA ASKED IF WE WERE DSNDING; AND I SAID 'YES.' HE THEN REPLIED TO 'JUST DSND AND MAINTAIN FL240.' WE COMPLIED AND I QUERIED HIM AS TO WHETHER THERE WAS ANY PROB WITH THE ALT; AND HE SAID 'NO.' SUPPLEMENTAL INFO FROM ACN 541920: WE WERE ON THE SKEBR 1 (RNAV) STAR TO LAS. ATC ASSIGNED US TO CROSS MISEN AT FL240. I RESPONDED AND THE CAPT AGREED WITH THIS. THE CAPT CHKED THE FMC AND SAW MISEN AT FL240A. HE DID NOT CHANGE THIS TO A HARD XING ALT. THE FMC PROCEEDED BASED ON THE OTHER HARD ALT. IT DID JUST AS WE HAD READ IN THE READ BEFORE FLY. THE CAPT WAS FLYING AND I LEFT THE FREQ TO GET ATIS. HE STARTED DOWN FROM FL290 AND OUT OF FL265 ATC QUESTIONED OUR XING ALT AT MISEN. THE CAPT INCREASED THE RATE OF DSCNT AND WE CROSSED MISEN AT FL250. ATC ADVISED US THAT WE DID NOT CONFLICT WITH ANY TFC. THIS EVENT SHOULD NOT HAVE HAPPENED BECAUSE WE HAD BOTH READ THE READ BEFORE FLY FILE WARNING US ABOUT THE SKEBR ARR. HOWEVER; IT IS STILL THE CREW'S RESPONSIBILITY AND I WILL BE MORE VIGILANT IN THE FUTURE.