A C172 pilot rejected his takeoff at SME after a helicopter entered the runway directly ahead. The helicopter did not acknowledge the C172 pilot's CTAF takeoff call.

Narrative

After announcing my intention to takeoff on Runway 5 on the SME UNICOM for a departure to the South West I entered Runway 5 and began my takeoff roll. After reaching about 40 KTS (55 KTS rotate speed) a helicopter entered the runway (5) at about halfway down the runway for his departure. He entered the active runway by 'air taxi' without hesitation and only announced his takeoff intentions on the UNICOM as he was entering the runway and was already over the runway before he finished his radio transmission. In order to avoid a collision; I pulled power to idle and braked; aborting my takeoff and proceeded to taxi back for a new takeoff attempt. Had the helicopter pilot paid more attention to the radio announcements on the UNICOM and looked down the runway he would have had a better situational awareness of the airport and the fact that there was an aircraft already attempting to takeoff on the active. Also; had he hesitated after his transmission before air taxiing onto the runway I would have had the chance to inform him as to my position before he proceeded further.