SEAN PENN'S CASTING CALL

CASTING TALL:

Sean Penn fought like a tiger to co-star three mentally retarded men in his new flick, "I Am Sam." Sean, who plays a mentally challenged dad doing his best to raise a daughter, spent weeks doing research at a facility that treats victims of the disorder and met three men he wanted to cast as his best pals in the film. Producers refused, saying the men couldn't handle the dialogue. Stubborn Sean went over their heads to studio brass, who finally caved in. Insiders say the scenes with Sean and his buddies are incredibly moving -- and the star's hours of work coaching them paid off big-time!