Lighting a game level saving baking

I have a simple test map with some objects that are textured and casting shadows on the wall. I want to render and save all the baked shadows and so on to the textures used.but when I hit the bake all my mesh goes black or my texture on the faces goes gray with the shadows on the gray texture on the mesh :(. I just wanted to be able to bake my details on to level textures so I can then load those textures with the shadows backed onto them in another program. can somone give me advice or give me a link to a tut on this??