Tim Castleman had a big response to the Sept. 11 attacks on the United States. He felt so sad, disappointed and angry that he changed his life. He started developing a hemp-based biofuel system and fought for legalization of hemp in Arizona to help end U.S. dependence on fossil fuels. He began a national "Drive 55" campaign to lower Americans' gas consumption and reduce carbon emissions — an effort turned into a documentary. And he organized two "Peace Trains" to Washington, D.C., to promote rail travel. "My interest in biofuels led me to understand the real problem isn't that we need another source of fuel. We need another source of energy," said Castleman, 51. "The real problem is we