From the FAQ posted at IMDB:
"Sin City is based on a series of black & white crime/drama comics created by Frank Miller"
"The leads for the stories are Mickey Rourke (Angelheart, 9 1/2 Weeks, Barfly) as "Marv" in the first segment followed by Bruce Willis (Die Hard, Moonlighting, 12 Monkeys) as "Hartigan" in the second with the third segment featuring Clive Owen (The Bourne Identity, Gosford Park, King Arthur) as "Dwight"."
"We will meet Kevin (Elijah Wood), an angel-faced mute with an affinity for wolves and a taste for human flesh. Then there's "Iron" Jack Rafferty (Benicio Del Toro from Traffic), hero cop and all-around scumbag. Also, there is Jr. Roark (Nick Stahl from Terminator 3), degenerate spawn of the powerful Roark empire"
"[Robert] Rodriguez is currently sharing directorial duties with Frank Miller and Quentin Tarantino."
"As per Rodriguez's preference, Sin City will be shot in high definition video, not film, and then digitally changed to black & white with spot color added here and there for visual effect"