Editor's note: Actor and environmental activist Ed Begley, Jr., journeyed last month in a natural-gas car from his hometown of Los Angeles to Des Moines, Iowa, site of the nation's first political caucuses, to raise the profile of clean-car technology. Here he relates his (mis)adventures. Ed -- happier in a tree than in a car. A Week Before Departure The good folks at the EarthYear 2000 event in Iowa are excited that I'm driving an alternative-fuel vehicle to their conference. They intend to put it on display for all to see. I love promoting clean technology. I've driven cross-country about …