It's fair to say that it's a risky venture create a movie about an exotically colored, 10-foot-tall tribe called the Na'vi and spend more money making it than any other film in the history of Hollywood. Yet investing hundreds of millions of dollars in James Cameron's "Avatar" (exact figures aren't available but the total cost, including marketing, is expected to run close to half a billion dollars) is a bet likely to pay off for 20th Century Fox.