DWG/DXF Converter is a shareware software, only $45, that allow you to convert DWG and/or DXF files version 12 to 2007 on DWG and/or DXF files version 12 to 2007.
So you can very simply convert a DWG 2007 file to a DWG 12 file or to a DXF 2000 file.
Download DWG/DXF Converter for Mac OSX or for Linux and try it.