MD80 FLT CREW; UNFAMILIAR WITH FMS ON ACFT; PROGRAM IT INCORRECTLY AND ARE UNABLE TO ENGAGE LATERAL NAV ON THE HOLTZ RNAV SID FROM LAX.

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ON THE HOLTZ 7 RNAV DEP OUT OF LAX THE NAV WOULD NOT ENGAGE AT 400 FT. AFTER TROUBLESHOOTING THE PROB DIDN'T WORK AND AT APPROX 1200 FT; WE TOLD DEP OUR NAV FUNCTION WASN'T WORKING AND THAT WE NEEDED A HDG. WE BELIEVE THAT WE STAYED ON COURSE DURING THE TIME BEFORE RECEIVING THE HDG; BUT CANNOT BE SURE. THERE IS A CHANCE THE AIRPLANE SYMBOL ON THE NAV DISPLAY WAS A FRACTION OFF OF THE MAGENTA LINE. DEP CTL GAVE US A HDG AND WE RESUMED OUR DEP. THEY NEVER MENTIONED THERE BEING A PROB. WE LATER DISCOVERED THAT THE PERFORMANCE 'INIT' PAGE ON THE FMS WAS NEVER COMPLETED DURING PREFLT PREPARATIONS; THUS NOT ALLOWING THE NAV TO ENGAGE. NEITHER THE CAPT NOR I HAVE FLOWN THIS TYPE OF AIRPLANE MUCH; THUS CONTRIBUTING TO THE 'CONFUSION' OF LOADING THE BOX. WE CHKED THE LEGS PAGE; RTE PAGE; AND TOTAL DISTANCE LIKE WE ARE USED TO; BUT THERE IS NO REQUIREMENT TO CHK THE PERFORMANCE 'INIT' PAGE; THUS WE BOTH MISSED IT. THERE WAS NO INDICATION ON THE MESSAGE LINE OF THE BOX THAT ANYTHING WAS AWRY UNTIL WE WERE IN THE AIR AND TRYING TO ENGAGE THE NAV; THAT'S WHEN IT SAID 'NAV/PERFORMANCE UNAVAILABLE.' BOTTOM LINE; WE BOTH SHOULD HAVE KNOWN AND DOUBLECHKED THAT ALL OF THE ACFT NAV INFO WAS LOADED PROPERLY.