Since AutoCAD 2002 the AutoCAD R14 DWG has not been a built in option. You can still convert your drawings to the R14 format for free.

Can only be used with AutoCAD 2004-based products, AutoCAD 2005-based products, AutoCAD LT 2004, or AutoCAD LT 2005.

Converter converts any AutoCAD® drawing file to AutoCAD® Release 14, AutoCAD® 2000, AutoCAD® 2000i, AutoCAD® 2002, AutoCAD® 2004, and AutoCAD® 2005 file formats. Batch Drawing Converter allows conversion of pen widths to lineweights and the addition of page setups.

Supported Products
AutoCAD® 2004 and later
AutoCAD LT® 2004 and later
Autodesk Map™ 2004 and later
Autodesk® Mechanical Desktop® 2004 and later
Autodesk® Architectural Desktop 2004 and later
AutoCAD® Mechanical 2004 and later
Autodesk® Building Systems 2004 later
Autodesk® Land Desktop 2004 later

http://www.autodesk.com/migrationtools