This video explains my process for re-working a model in SU, and re-importing it into Max, but using the materials that I have already created for the original model. It may not be the most elegant process, but it works and saves me alot of time.
A couple of side notes:
-If I import as .3ds file, I scrap the texture maps from SU, and apply a UVW modifier with realworld coordinates to all of my meshes....this way I always remember how to reapply my UV's on a new import and the old materials will still work.
-If my sketchUp files have texture maps and are imported as a .skp I use the existing UV coordinates from SU