The pilot's failure to maintain clearance from the terrain while attempting to fly a non-IFR equipped aircraft solely by reference to its instruments after the aircraft's windshield became coated with freezing rain in cruise flight. A factor was the pilot's improper inflight decision to continue VFR flight in an area where rain showers where taking place while ambient temperatures where indicated to be within one degree of freezing. Additional factors include freezing rain, an iced-over windshield, and tree-covered rising terrain.