1. A KML-file can be made with Google Earth or at maps.google.com.
2. You can use kml-file of maps.google.com with the network link (see demo).
3. The kml filename must be all lower case. For example, 'map1.kml' NOT 'Map1.kml'.
4. Upload the kml-file at a directory on your webserver where visitors of your site and Google has access to.
5. Check the kml-file at maps.google.com if it show allright.
6. Check the kml-file at the kml-validator .
   
7. Remember that the parameter lon, lat and zoom level of the plugin define the starting view. Leave them empty so the plugin will zoom in to the right view for the kml-file.
   If you enter lat, long and zoom as starting point in Europe, then it will appear as though our US map is not functioning properly.  But if you zoom out or move to US then the kml will show up.
8. Don't forget to change the template for showing polyline (see: checklist ) otherwise there will be no line when showing a KML-file.
9. A KML-file is rendered by Google! Google uses a cache so it can quickly reproduce a rendered kml-file for other visitors. If you change the content of the kml-fle it will take a while before the changes will be shown on your site. Rename the kml-file to a new name to see direct results.
10. Sometime you have to set the mime type of the kml or kmz files to make it work
    For apache, add these lines to the httpd.conf file or a .htaccess file in the same directory as the kml/kmz-file:
    * AddType application/vnd.google-earth.kml+xml .kml
    * AddType application/vnd.google-earth.kmz .kmz
    For linux:
    * AddType application/vnd.google-earth.kml+xml .kml
    * AddType application/vnd.google-earth.kmz .kmz
    Application: opt/google-earth/googleearth
    
11. More information or support on kml-files have a look at: http://groups.google.com/group/kml-support.

You can use Docman to upload the kml files at the frontend of Joomla. The parameter kml has to be entered as kml=http://www.sitename.com/docs/filename.kml. 

The KML-file can be to big to handle for google.