Autodesk Inventor supports import of IGES format (.igs, .iges) just fine and can use the data to create a new Inventor project and save it as .idw drawing file. Without Inventor it might actually be very tricky to achieve igs to idw conversion, because unfortunately not many programs support Inventor formats. You may have luck with some dedicated CAD/3D modeling converters.
Open IGS file Open IDW file