In order to process 3D models on AUTOCAD you need to have Land Development Desktop 2004. The Land Development Desktop 2004 has AutoCAD engine built into it. AUTOCAD 2004 is just a basic drafting tool.
It is a contouring program that runs inside autocad. I'm not sure about 2004 compatibility, but it seems to run well under 2002. I believe they have a free trial. It will do more than contours, cut fill, road design, but I haven't used these features, so I don't know much about them.