More than 30 billionaires have agreed to donate at least half their fortunes to charity; the list was made public yesterday. The Giving Pledge Campaign is the brainchild of Microsoft founder Bill Gates and investor Warren Buffet. It now has pledges from New York Mayor Michael Bloomberg, media mogul Ted Turner, filmmaker George Lucas, and dozens more. Forbes Magazine is estimating at least $150 billion could be donated. Wall Street and finance reporter for The New York Times, Louise Story, has the details of this new venture by some of the country's richest people.