Craig will play the role of Mikael Blomkvist, a disgraced journalist who gets caught up in the search for a woman missing for forty years, while being aided by an eccentric young female hacker. The role of Blomkvist was played (close to perfection, in my opinion) by Michael Nyqvist in the Swedish version of the film (see pic below).
Getting Craig in the film was reportedly something of a juggling act, since the actor has two other franchise properties on his plate, currently. There is of course the James Bond franchise, which is currently stalled over at MGM; Craig is also attached to Jon Favreau's adaptation of Cowboys & Aliens, which is set up over at Dreamworks.
Sony reportedly worked out an agreeable schedule with the other two studios, allowing Craig to star in Dragon Tattoo with options to star in the two sequels, which complete the Millennium Trilogy. Movie adaptations of the other two books, The Girl Who Played With Fire and The Girl Who Kicked The Hornets' Nest have already been made in Sweden.
I'm pretty sure that when rumors of Craig's attachment to this remake were first floated, the general consensus was that he'd be a pretty good choice to play Blomkvist. In fact, having Craig in the leading role and David Fincher at the helm are pretty much the only reasons why this remake isn't getting slammed around the blogosphere. Early favor toward this remake now rests squarely on the actress who is cast as Lisabeth Salander. More on that as it unfolds.
The Girl With The Dragon Tatoo is slated for release on December 21, 2011.