During his pre-landing checks, the pilot found the landing gear manual extension handle was difficult to move toward the "gear extended" position. After returning the handle to the "gear retracted" position he was able to move it, with some difficulty, to the extended position. However, in order to reassure himself that the system was functioning correctly, the pilot carried out a missed approach to undertake further checks. He successfully completed a number of landing gear retractions and extensions, but still experienced the same difficulty as previously found. He then returned for a landing. During final approach, the pilot recalled hearing a warning horn, but believed it was the stall warning horn and decided to apply more power to maintain what he considered a safe approach speed. The warning horn continued, distracting the pilot from his final approach checks. He continued to believe he was listening to the stall warning but was puzzled that he was still able to hear it, given the speed and configuration of the aircraft. He realised the landing gear was still retracted when he heard the underside of the fuselage scraping along the runway during the landing. The horn he had heard during the approach was the landing gear unsafe warning. The pilot's pre-occupation with the warning horn on final approach, and his concern about the stiffness of movement of the landing gear handle, are considered to be factors contributing to the development of this occurrence.