SketchUp > Blender

Here is the process of going from SketchUp to Blender 3D:
http://www.katsbits.com/htm/tutorials/sketchup_converting_import_kmz_blender.htm

When finished, you may want to go through this process as well:
http://www.blendercookie.com/2009/12/29/tip-cleaning-up-imported-models/