On May 12, 2004, about 1145 central daylight time, a Robinson R22 Beta helicopter, N2301F, piloted by a commercial pilot, sustained substantial damage duirng a forced landing following a failure of the main drive belts near Winsted, Minnesota. The 14 CFR Part 91 personal flight was operating in marginal visual meteorological conditions without a flight plan. The pilot, who was the sole occupant, received minor injuries. The origin of the flight has not been determined. The pilot initially reported to a Federal Aviation Administration (FAA) Inspector that he heard a loud bang, smelled rubber, received a clutch warning light, and autorotated to a recently planted corn field. The pilot has not submitted a written report of the accident. The FAA Inspector that responded to the accident site reported that the corn was approximately 2 inches tall in rolling terrain. Pictures of the accident site confirmed the terrain condition. The tail rotor and aft section of the tail boom were separated from the helicopter and the landing skids were bent outward and upward. The main drive system was examined. The main drive belts are composed of 2 independent belts each having twin V's. The 2 belts run in 4 groove pulley sheaves attached to the engine and clutch. One of the belts was split between the 2 V's for approximately 1/2 of the circumference of the belt. The second belt was shredded. Examination of the actuator revealed no anomalies. No other anomalies could be found with respect to the drive system.