For a description of the Bump 2D utility, see Bump 2d.
To bump map layered textures using Provide3d Info
To cascade, or stack, bump maps
Maya provides a MEL script that does this for you. After you connect the Out Color of the environment map to the Reflected Color of the material, type cnctBumpProjNormal shader-name in the command line (where shader-name is the name of the material).