The single-engine airplane nosed over while landing on Runway 35. The 27,500-hour airline transport pilot landed the single-engine airplane on the 2,450-feet long, by 55-feet wide turf runway. The pilot reported that when he lined up for the straight-in approach and landing, he noticed that the northern half of the runway appeared to have been graded; however, he failed to notice the large white X on the approach end (south) of the runway. The pilot further reported that the touchdown and landing roll was normal about 500 to 600 feet down the grass portion and when the aircraft entered the graded area the airplane bounced slightly, slowed, then "flipped over on it's top." The pilot and his three passengers were able to egress unassisted with two passengers receiving minor injuries during the accident sequence. The airplane sustained structural damage to the nose landing gear, fuselage, and wings. The pilot stated on the NTSB Form 6120.1 that prior to departure he checked the weather and the airport information on airnav.com on the Internet. He also added that the NOTAM section would not open on the web site and did not check any other sources. Weather reported from an airport located 15 miles to the south was winds calm, skies clear, temperature of 20 degrees Celsius, and an altimeter reading of 30.13 inches of Mercury.