You have to add textures in Bryce to different channels in the material editor like the bump map and if you need it, the ambiance channel. And you dont
Have to use both black and gray. You can just use the gray if you like
But as I have said before, Renderosity and the Bryce forum, or this site has some nice tuts in Bryce
http://www.brycetech.com/ Those are a good source for learning the ways of the render
Here we just model and uv-mapp