The airplane stalled and impacted the runway while landing. The pilot reported that while en route a passenger stated that he was ill. The pilot contacted air traffic control and diverted to a nearby airport. The pilot reported he initiated an ILS approach and told a pilot rated passenger to "report the runway in sight." The pilot stated, "He called my attention to the runway ahead. I saw it and continued the descent." The pilot reported that when over the runway at an altitude of 20 feet, the airplane stalled and impacted the runway. The accident airport weather conditions reported 12 minutes after the accident, were visibility less than 1/4 mile with fog, and a 100 foot indefinite ceiling. This information was being broadcasted over the airport Automated Surface Observing System (ASOS). The ceiling and visibility had not changed during the time period starting one hour prior to the accident to two hours after the accident. The pilot reported the weather as being 1/2 mile visibility with a 200 foot overcast ceiling. The minimums for the ILS approach were 1/2 mile visibility and a 200 foot ceiling.