THE PLT RPRTD THAT WHEN HE WAS ON FINAL APCH TO LAND, THERE WAS A LEARJET BEHIND HIM ON A 5 MILE FINAL APCH. HE STATED THAT HE MADE A NORMAL LANDING, THEN STEERED LEFT TOWARD THE 'TAXIWAY SIDE' OF THE RWY TO EXPEDITE OFF THE RWY. HOWEVER, AFTER REACHING THE LEFT SIDE, HE WAS UNABLE TO ALIGN THE ACFT BACK ON THE RWY HEADING & ELECTED TO CONTINUE OFF THE RWY, RATHER THAN RISK GROUND LOOPING THE ACFT. AFTER DEPARTING THE RWY, THE ACFT ENTERED SNOW & NOSED OVER. NO MECH MALFUNCTION OR FAILURE WAS RPRTD.