WHILE EN ROUTE FROM SACRAMENTO TO ARCATA, CA, THE PLT CONTACTED ARTCC & FILED AN IFR FLT PLAN. AS HE WAS APCHG THE DESTN AT 10,000', HE REQUESTED A LOWER ALT. HE WAS CLEARED TO DSCND TO 8000'. HE WAS THEN CLEARED FOR AN ILS RWY 32 APCH TO AN UNCTLD ARPT AT ARCATA WITH A RESTRICTION TO REMAIN AT 8000' UNTIL CROSSING THE YAGER INTXN. THE PLT BGN HIS DSCNT EARLY & CROSSED THE YAGER INTXN AT 6700. THE ACFT DSCNDD BELOW RADAR COVERAGE AT 5300'. RADAR SVC WAS TERMINATED & THE PLT WAS INSTRUCTED TO CONTACT THE ARCATA FSS. HE CONTACTED THE FSS STATION & WAS ADZD THE WX WAS PARTIALLY OBSCD, 400' BKN, 1500' BKN, 2400' OVC, 3 MI VIS. THE PLT ACKNOWLEDGE & SAID HE WAS IN THE CLOUDS AT 3200', THEN THERE WAS NO FURTHER CONTACT WITH THE ACFT. A SEARCH WAS INITIATED & THE ACFT WAS FOUND WHERE IT HAD CRASHED ALONG THE ILS COURSE LINE ABOUT 18 MI SHORT OF THE RWY. IMPACT OCCURRED ON HILLY/MOUNTAINOUS TERRAIN AT AN ELEV OF ABOUT 2750'. THE MIN DSCNT ALT FOR THAT SEGMENT OF THE APCH WAS 5200'.