Apart from that... I believe google sketchup was able to handle DWG but I do not know if it will be able to exchange with AutoCAD. Or at least I assume that's the reason why you want *.dwg compatibility.
Autodesk and "free"? They'll need to look that up in their dictionary.
You could get a free version of any AutoCAD '09 if you are a studying anything that involves autoCAD on a recognized university and you have access to a school email address of that uni. I guess you do not have that though