ALTDEV ALT UNDERSHOT IN MISSED ALT XING RESTRICTION.

Narrative

DEPARTED SAN-LAX FLT NORMAL. GIVEN SID TO VOR. CRUISE ALT WAS 10000 FT MSL. AT CRUISE ALT WE WERE GIVEN DIRECT VOR. STILL 50 NM SW OF VOR FIRST FLT ATTENDANT ADVISED SHE HAD A BURNED OUT LIGHT AT HER STATION. BEING THE CAPT'S LEG AND PF; I TOOK THE PNF ROLE AND PROCEEDED TO DO THE CABIN RIGHT UP. APCH GAVE US A CLRNC TO 7000 FT MSL 10 SW VOR. APPROX 25 MI FROM VOR. I WAS BUSY DOING THE LOGBOOKS AND WHEN I FINISHED I NOTICED WE WERE 20 MI FROM VOR AND DOING 300 KTS. AT 10000 FT. I ASKED THE CAPT WHO WAS BUSY TRYING TO PUT THE POINT 10 SW OF VOR IN OUR FMC; IF HE REALIZED WE WERE 10 NW FROM OUR 7000 FT MSL CLRNC. HE STATED 'YEAH; I'M TRYING TO PUT THE POINT IN.' AFTER AN UNSUCCESSFUL ATTEMPT I TOLD HIM HE BETTER START DOWN TO MEET OUR XING POINT. AT THIS POINT HE REALIZED HE WAS GETTING CLOSE AND STARTED DSCNT. AT 9950 FT I ASKED HIM IF HE KNEW WE WERE STILL GOING 300 KTS; HE REPLIED THAT HE 'FORGOT!' PF PUT OUT SPD BRAKES AND SLOWED TO 250 KTS BY 9400 FT MSL AND WE MISSED OUR XING ALT BY 2 NM. I ASKED AND DID GET RELIEF FROM APCH CTL ON THE XING SAYING 'IT MAY BE TIGHT.' APCH RECLRED US TO CROSS VOR AT 7000 FT INSTEAD. REST OF FLT WAS UNEVENTFUL. CAPT HAD PREVIOUS EXPERIENCE IN 'GLASS COCKPIT' ON B-757 BUT HAD DIFFICULTY ON THE B-737-300 I BELIEVE HE WAS LETTING THE COMPUTER DO THE THINKING INSTEAD OF HIMSELF FLYING THE AIRPLANE. IT WAS ALSO A LONG DUTY DAY 7:45 MINUTES FLYING TIME SCHEDULED. 13 HRS DUTY DAY. WE WERE BOTH TIRED. I HAVE ALWAYS HEARD OF NOT DOING NON-ESSENTIAL PAPER WORK BELOW 18000 FT MSL AND FROM THIS RPTR - I NOW KNOW WHY. I WAS DISTRACTED FILLING OUT LOG WHICH COULD HAVE WAITED UNTIL ON GND. IT TOOK AWAY MY ATTN FROM OUR XING FIX. NEVER AGAIN. THIS ALL COULD HAVE BEEN AVOIDED IF I WAS NOT DOING THE LOG. IF PF WAS AWARE OF OUR POS AND SPD AND PF WAS NOT TRYING TO PUT WAYPOINT INTO FMS.