I replied extensively to a post about this not long ago but try googling this. It's going to take place between RE2 and RE3 and played through either the umbrella corporation or I believe a government entity. Interesting twist and allows you to re-create history.
As already stated it will be labeled RE:Op Racoon City. i do believe it will not strictly be a co-op game as that would be rather ridiculous... but it is heavily built for co-op play.