Google Maps can now read KML or KMZ, the file formats Google Earth uses for the exchange of geographic information. This means that you can view data you create and share with Google Earth on Google Maps. You can use this feature to plot multiple points of interest, draw lines, and mark regions on Maps. Just paste the URL that hosts your KML file into the Maps search box and click Search. In order to share this map with others, click the link icon () on the left-hand side of the page. Take a look at this example.
Google Maps currently supports KML files with points, lines, polygons, styles, icons, and network links (without view-based refresh). We also support ground overlays, screen overlays, folders, and visibility. You can find more information about creating your own KML file at this Google Earth page.
Keep in mind that your KML file must be hosted on a website to view it in Google Maps. If you'd like to check out some of the KML files already on the web, you may want to start at the discussion forum for Google Earth, the Google Earth BBS.
If you are have a KMZ file, please use ZIP 2.0 or "legacy" compatible compression. Otherwise, the .kmz file might not uncompress in geo-browsers such as Google Earth. Using the more advanced compression methods (e.g., bzip2, LZMA, etc.) will not be compatible.
For more detailed information on how to add a Google Map to your site, visit http://maps.google.com/help/maps/getmaps