In Bryce, 'create' a wall with one of the create objects, then 'edit' the wall by selecting the surface you want (rocks, etc.). Make the wall fill your window, render it and 'save as' a file that you can open in Poser, such as TIFF. In Poser, create a surface (one sided square, etc.) and go into 'render' and 'materials' and select the file you just saved in Bryce. When you render, you have your textured wall. This will work for anything you can create in Bryce as a surface, then 'save as' in a format compatable with Poser textures.