Autodesk DWG TrueView is a free viewer for AutoCAD DWG/DXF files. Since Autodesk developed the DWG file format, using DWG TrueView to view and print AutoCAD files ensures that the integrity of the file is maintained.
Autodesk DWG TrueView can be downloaded here.
In addition to TrueView, a DWG Converter for converting DWG files between different versions of AutoCAD will be available in November. Check http://www.autodesk.com/dwgtrueconvert for more information about this product as it becomes available.