I went and uploaded a bunch of Planescape: Torment backgrounds to
FileFront to be used as a reference for those working to create textures, architecture, etc. for the Planescape setting. The images are very large and detailed so be sure you view them at 100% size as most picture viewers will automatically scale them down.
There's a gallery of some sample images from the set
HERE, though much lower in resolution, to give you an idea.