ArcObjects VBA code to take a feature layer, split it up into line segments, and then generate a valid KML file. It’s pretty basic, and you have to hard code some values, but it does the job. It will work with either lines or polygons, and it shouldn’t matter whether it’s a shapefile or a coverage. Just make sure that your layer is projected into lat/long first.
Looks like Jim’s code is now on ArcScripts.