hi, thanks for the feedback
I'm going to assume that you are probably running Inkscape 0.46, the stable release.
In this case, you'll need a different version of the .inx file. You will need to take the attached file, dxf_input_46stable.inx, rename it to be dxf_input.inx, and save it in the directory C:\Program Files\Inkscape\share\extensions\ to replace the existing file that is there.
If all goes well, then when you try to use File | Import or File | Open, and if you check the file types, there should be a file type "AutoCAD DXF (*.dxf)"
hope this helps, and feel free to submit any .dxf files that are not performing as expected