If your a student Autodesk has several programs that can be downloaded free with a 3 year licence. These are full version professional programs. I would recommend downloading Inventor Professional which I have, this is a $6,000 program. The only thing different on the student versions is that any drawings you print will have "this drawing was created with a academic version of Inventor". The text is outside the border of the title block / drawing sheet where it could be trimmed off. This program will read and write .stl 3d files as well as .dxf for 2d files and would work perfect with both the Stl Importer and Dxf Importer.
Here is a link to the Autodesk download site:
http://www.autodesk.com/education/free-software