B737-300 FLT CREW WAS CLEARED FOR AN ILS APCH. DME WAS OTS AND THE FLT CREW INITIALLY DESCENDED ON A 'FALSE' GS; PLACING THEM 500 FT LOW AT THE OM.

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AS WE WERE ON ARR INTO MCO; THE ATIS GIVEN INDICATED THEY WERE LNDG S. WE BRIEFED THE RWY 35R APCH AND THEN NOTED THE DIFFERENCES IF WE WERE TO LAND ON RWY 36L. AFTER BEING SWITCHED TO APCH CTL ABOUT COSTR INTXN; WAS ADVISED NOW LNDG RWY 18R. WE REPROGRAMMED THE FMC FOR RWY 18R. WE WERE STILL ON THE LNAV FOR COSTR ARR. WE WERE GIVEN AN EASTERLY HDG AND A DSCNT. WE SWITCHED TO VOR MODE. NOTICED DME NOT WORKING FOR RWY 18R. CHKED IDENT ON LOC FREQ AND HAD GOOD IDENT WITH NO INDICATION OF DME OUTAGE. GIVEN ANOTHER HDG AND DSCNT. INQUIRED TO ATC ABOUT DME INOP ON RWY 18R. HE SAID THAT THAT WAS THE FIRST RPT HE HAD; SO I FIGURED WE HAD AN EQUIP FAILURE. I SELECTED THE MCO VOR QUICKLY TO VERIFY DME FUNCTIONALITY ON ACFT AND IT WORKED OK. I SWITCHED BACK TO ILS FREQ AND DID NOT HAVE DME FOR THE FREQ. DURING THIS TIME APCH GAVE US A FINAL HDG TO INTERCEPT AND ANOTHER DSCNT. THE FO ARMED THE VOR/LOC APCH MODE. THE FO NOTED THAT THERE WERE NO POINTS IN THE FMC FOR RWY 18R EXCEPT FOR THE FAF AND RWY 18R AND THE MISSED APCH POINTS. I THEN TRIED TO REPROGRAM THE FMC TO OBTAIN THE OTHER FIXES. I PUT IN RWY 18R AND AGAIN ONLY THE FAF AND RWY 18R AND MISSED APCH POINTS WENT IN. NONE OF THE OTHER POINTS ALONG THE EXTENDED LOC WERE IN THE FMC. WHEN I LOOKED UP; THE ACFT HAD FLOWN THROUGH THE LOC. I DIRECTED THE FO TO FLY TO THE R TO RE-INTERCEPT AND CALLED ATC AND NOTIFIED THEM THAT WE WENT THROUGH THE LOC. HE GAVE US A NEW HDG TO INTERCEPT AND ANOTHER DSCNT. WHEN THE FO RE-ARMED THE VOR/LOC MODE; THE ACFT STARTED TO TURN L TO INTERCEPT. HE DISCONNECTED THE AUTOPLT AND WENT BACK TO THE R TOWARDS THE LOC. TOLD TO MAINTAIN 3000 FT TO HAMMY. WE HAD NO WAYPOINT FOR HAMMY IN THE FMC AND NO DME TO IDENT THE FIX. ATC THEN CAME BACK AND SAID THAT THE DME WAS OTS. FINALLY INTERCEPTED THE LOC AND WAS GIVEN A DSCNT TO 2300 FT TO TUFFE. ABOUT THIS TIME THE GS CAME IN AND WE STARTED DOWN THE GS. AT SOME POINT ABOUT THIS TIME ATC ASKED US IF IT WAS TOO LATE TO SWITCH TO RWY 17R. GOING DOWN THE GS AT ABOUT 1700 FT; THE GS QUICKLY WENT FULL SCALE UP. WE DID NOT HAVE AN ABNORMAL SINK RATE AT ANY TIME. I TOLD THE FO TO LEVEL OFF AND WE WERE AT ABOUT 1700 FT. BY THIS TIME WE WERE ABOUT TUFFE AND ABOUT 500 FT LOW BUT NOW IN VMC AND HAD THE FIELD IN SIGHT. THE GS CAME BACK INTO 'ON' GS INDICATION. THE LNDG AND TAXI IN WERE UNEVENTFUL. IF WE HAD NOT BEEN IN VMC WHEN WE REALIZED OUR ALT AND WHEN THE GS WENT QUICKLY FULL UP; WE WOULD HAVE GONE MISSED APCH. APCH WAS WORKING MULTIPLE ACFT WITH MULTIPLE EQUIP FAILURES AT THE FIELD. RWY 17L GS OTS AND THEN THE DME FAILURE FOR RWY 18R. THE APCH CHART INDICATES THAT DME OR RADAR IS REQUIRED. WHEN THE DME WAS OTS; I'M NOT SURE IF ATC TRIED TO RESET THE ILS FOR RWY 18R WHICH CAUSED THE GS DEV WE EXPERIENCED. I NEVER SAW A GS FLAG DURING THE APCH.