According to TDN, that serves the Columbia Valley, the Twilight movie will be using Kalama High School as a shooting location during the school’s spring break. Whether or not Forks High School will be used at all is not at this time known. They may use Forks HS for exterior shots, but this high school for interiors.
Also, while I am at it, yes we are aware of the rumors circulating around the net. At this time they are just that–rumors. I wouldn’t put too much stock in anything until it is officially released by Stephenie or Summit. In other words, do the words "Colton Haynes" and staying up until 3:00am for Tory’s big announcement ring any bells?
Lastly, the fact that Summit is having an open casting for Jacob Black does not mean other parts have not been cast. It means they just haven’t announced it. Remember that movies are not shot in chronological order. Jacob has a small part in Twilight. It is not a big deal not to have that part at this point.