For reasons that I still can only hazard guesses at (most of the guesses would have to do with profit potential), it is not uncommon for major movies to be released in novel -or even comic book- form before they actually reach the big screen audience. X-Men 3 the novel is set for release on May 16th, which beats the movie release date by about a week and a half. TrekWeb has a brief plot synopsis of the book (and presumably therefore the movie as well) here. The novel, based on the screenplay, is written by Chris Claremont and is approximately 350 pages.
Oh yeah, and the link provided also shows off a new image from the film showing the good Professor in a casual situation with a few of his students, if you're interested. At least, they claim it is a new picture- how anyone can keep track at this point is beyond me. I think I reached my maximum X-Men picture interest roughly sixty-one thousand and five pictures ago. But that's probably just me.