''Spider-Man 2'' won't hit the screen until July 2, but distributor Sony and comics house Marvel are already at work on the third installment of the superhero franchise. Marvel Studios chief Avi Arad mentioned ''Spider-Man 3'' briefly in a conference call to financial analysts and reporters on Tuesday. He was cryptic about the details of the sequel, save for the projected release date. ''[The] best case scenario I can tell you [is] 2006,'' he said. ''It is a big movie, and we would rather play it safe and talk about 2007 at this point.'' According to Variety, there's no script yet, but Sam Raimi (who directed the first two installments) is reportedly committed to shooting the third, and star Tobey Maguire has been keeping his schedule open for a shoot next year.