Witnesses observed the takeoff roll as being unusually long. The acft never climbed much above 100-200 ft agl, & struck trees 1/2 mi off the end of the rwy. The flaps were observed up during takeoff. Normal takeoff flap setting used by the club for carrying jumpers is 10 deg. The acft was 166 pounds over max gross weight & the cg was beyond the aft limit. The density altitude was approximately 2,000 ft. The plt had never flown a c-182 or a constant speed propeller equipped acft prior to his checkout with the parachute club the week before the accident. The day of the accident was the first time he had carried any jumpers. The plt had agreed to fly for the club for no compensation other than to build flt time.