SAFETY PLT ABOARD A BE76 DURING AN IAP PRACTICE FLT IS DISTR AND LOOKS UP TO FIND THE PLT HAS DSNDED 1000 FT BELOW HIS ALT REQUIRED BY THE LOC ONLY APCH TO RWY 32 AT STP.

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WE WERE INBOUND ON THE ILS-32 AND CLRED FOR THE APCH. WE WERE GIVEN AN ADVISORY BEFORE COMMENCING THE APCH THAT THE GS WAS OTS. THE APCH STATED TO MAINTAIN 2500 FT MSL UNTIL THE FAF. AS WE WERE ESTABLISHED INBOUND; WE WERE HANDED OVER TO THE TWR. SINCE WE WERE PRACTICING INST APCHS WITH ARPTS RELATIVELY CLOSE TO EACH OTHER; THERE WAS A HIGHER WORKLOAD. WITH EACH APCH CONCLUDING AT A MISSED APCH AND ONTO A DIFFERENT ARPT FOR ANOTHER INST APCH. THE APCH WAS LOOKING GOOD AND I USED THE EXTRA TIME TO GET THE NEXT CHART READY FOR THE NEXT ARPT FOR THE PF. AS I LOOKED UP FROM THE CHART; I NOTICED THAT WE WERE ABOUT 1500 FT MSL AND THE ARPT WAS ABOUT 7 MI AHEAD OF US. THIS PUT US 1000 FT BELOW OUR REQUIRED ALT AND ABOUT 2 MI BEFORE THE FAF. I THEN TOLD THE PF OF THE ERROR AND TOLD THE PLT TO CLB BACK UP TO 2500 FT MSL. AT THE SAME TIME AS WE WERE CLBING BACK UP TO ALT; WE GOT A CALL FROM THE TWR SAYING THAT THEY GOT A LOW ALT ALERT FOR OUR AIRPLANE AND THEY ALSO TOLD US WHAT OUR REQUIRED ALT WAS. WE CLBED BACK TO 2500 FT MSL AND COMPLETED THE APCH WITHOUT INCIDENT. CONTRIBUTING FACTORS WAS MY ATTN BEING DIVERTED TO AN UNNECESSARY TASK FOR THE GIVEN SITUATION AND FAILING TO MONITOR THE APCH. ALSO; THE PF MISTAKE OF FOLLOWING A GS THAT WAS OTS. THE PF ALSO MENTIONED THAT A GLIDE SLOPE FLAG WAS NOT NOTED ON THE VOR. ADDITIONAL HUMAN ERROR FACTORS COULD HAVE ARISEN THROUGH THE LONG PRACTICE SESSION THAT WAS BEING CONDUCTED. I HAVE LEARNED THAT IT IS EXTREMELY IMPORTANT TO ONLY CONCENTRATE ON THE TASK AT HAND; EVEN IF ANOTHER PLT IS FLYING. ALSO ONE CAN NEVER DO ENOUGH CHKING AND DOUBLECHKING. WHICH WOULD INCLUDE ALWAYS DOUBLECHKING THE ALT TO BE AT AND DOUBLECHKING THAT WE ARE IN THE PROPER PLACE AND POS TO DSND DOWN TO THE NEXT ALT AS REQUIRED. FINALLY ALWAYS BEING CONSCIOUS OF WHAT COULD AFFECT THE FLT SUCH AS NAV EQUIP OUTAGES.