Don't do what I did: I couldn't get 4.1 to load, and Corel's direction recommended doing a clean load of Bryce 4. I did that without thinking, and I saw all my custom materials and skies get overwritten... Oh well, I can just open all of my old Bryce files and rebuild the library, its just going to be a lot of work. I should have copied the material and sky libraries to a different directory first.