The pilot's decision to continue flight into known icing conditions, and his subsequent failure to maintain adequate airspeed on final approach, resulting in a hard landing. Factors included: icing conditions; the pilot's improper decision to continue to his planned destination from an ILS low approach rather than to execute the straight-in ILS approach to a full stop on a more suitable runway for his flight situation; and the pilot's failure to follow proper pilot's operating handbook procedures for an inadvertent icing encounter.