A few weeks ago, a 23 year old atheist posted an unusual item for sale on eBay: a chance to save his soul. Mr. Hemant Mehta is a DePaul University graduate student who promised the winner that for each $10 of the final bid, he would attend an hour of church services. Evangelists bid, eager to save a sinner. Atheists bid, hoping to keep Mr. Mehta in their fold. When the auction stopped on Feb. 3 after 41 bids, the buyer was Jim Henderson, whose $504 bid prevailed. But Mr. Henderson wasn't looking for a convert; he wanted Mr. Mehta to embark with him on an eccentric experiment in spiritual bridge-building.