Have you tried using the layer translater? It's particularly useful if you get a drawing that has a slew of layers for objects you want all on one layer. For example, if someone sends you a drawing with curb on 10 different layers for some reason, and you want all the curb on a single "Curb" layer, the layer translater makes it easy.
You start up the layer translater in the drawing you want to change, load a drawing with your "good" layers in it to use as a template, and then map layers in your "bad" drawing to the layers in your "good" drawing.