As mentioned on http://www.righthemisphere.com/forum/announcement.php?forumid=50 , the old 2D version of Deep Paint has been discontinued. However, it was turned into a freeware application, which is a kind gesture. You can use it for painting, using a mouse or (even better) a Wacom Tablet. It has support for layers, has a direct link with Photoshop (but not the latest versions) and has some tools to introduce a bump-map effect (for which you can alter the lighting afterwards). Give it a try. It can be found on http://www.download.com/Deep-Paint/3000-2191_4-10398243.html . [Autodesk should have done this with the old LightScape]
Info on BIM, CAD & 3D software for architects and students