Converting KML into a vector graphic... and back

Some notes:

1. You'd need an editor which could work with geo coordinates instead of simple X,Y ones. Or you would need to reproject coordinates when converting.
2. Converting from KML to SVG would mean potentially losing KML-specific information which is not stored by the SVG format.
3. Converting from SVG to KML would mean potentially losing SVG styling and other features not covered in KML.
4. GIMP is not a vector graphics editor (AFAIK), you probably mean Inkscape.

Other than that, there are quite a few tools which claim to do what you're looking for.

Simple as in SVG to KML and KML to SVG?

This tool converts Google Earth files(kml and kmz) into vectorial SVG files, usable in Inkscape, Illustrator and other software.

kml2svg.free.fr converts most of the elements that contains a GE document:

folders
placemarks (points, lines, polygones, multigeometries and embeded images)
tours
Sketchup resources (depending of the resources..)

using the desired earth projection:

Mercator,
Miller,
Cylindrical Equal-Area (Lambert, Behrmann, Tristan Edwards, Peters, Galls, Balthasart),
Cylindrical Equidistant,
Sinusoidal,
Van der Grinten I,
Polyconic,
Albers Equal-Area Conic,
Conic Equidistant,
Bonne,
Lambert Conformal Conic,
Lambert Azimuthal Equal-Area,
Cassini

http://kml2svg.free.fr/

I wanted to get a geographic area from a KML file into Microsoft Visio. I got it working like this:

1. Open the KML file in the web app.
2. Get the projection in the way you want
3. Export to SVG file
4. Import the SVG file in Inkscape
5. Save the file as EMF file
6. Insert the EMF file in Visio as a picture

Visio supports insertion of SVG files, but for some reason it didn't work, so I had to go via Inkscape.