DRG A NIGHT ARRIVAL, THE PLT CONTACTED NAS POINT MUGU APCH CTL & WAS CLRD FOR A VOR RWY 26 APCH. AS THE PLT CONTD THE APCH, THE ACFT VEERED RADICALLY OFF COURSE TO THE RIGHT & DSCNDD PREMATURELY. THE CTLR ISSUED A SAFETY ALERT & TOLD THE PLT TO TURN LEFT TO A HEADING OF 210 DEG & TO CLIMB & MAINT 2100 FT. THE PLT ACKNOWLEDGED, BUT FAILED TO TAKE ADEQUATE CORRECTIVE ACTION. SUBSEQUENTLY, THE ACFT COLLIDED WITH MOUNTAINOUS TERRAIN AT AN ELEVATION OF ABOUT 1100 FT, AS IT WAS APCHG THE FINAL APCH FIX (FAF). MIN DSCNT ALT (MDA) ON THAT SEGMENT OF THE APCH WAS 2100 FT MSL. APRX 10 MI SW AT POINT MUGU (ELEV 12 FT), THE 2155 PST WX WAS IN PART: 1000 FT OVC, 6 MI VIS WITH FOG & HAZE. THE PLT HAD BEEN ISSUED AN INSTRUMENT RATING ON 4/28/89. SINCE THAT DATE, HE HAD LOGGED ONLY 5.5 HRS OF INSTRUMENT TIME & 4 INSTRUMENT APCHS.