You must have seen this, right? The Possession official site. It's Flash-heavy but worth it. There are some pretty photos in the "Stills" section I can't remember seeing before. They're all from scenes that were edited out of the film, I believe. First, one of Ash and Christabel descending outdoor stairs. Second, on a hike. Third, a behind-the-scenes shot. For some audio clips, click on "Explore".
Read A.S. Byatt's book too.