Sienna Miller has become the first big name to sign up for the new G.I. Joe movie. The film, based on the popular U.S. play figure and TV series, will start shooting in February, with a release date scheduled for summer, 2009. The Mummy director Stephen Sommers will take charge of the film, while Miller will play the femme fatale known as the Baroness, according to Daily Variety. The casting of the title character has yet to be announced.