Now, to add the finished map to your site.. Look in the upper right corner of the map..
Click on "Link to this page", which changes the URL in the address bar up top from the "regular" http://maps.google.com/maps to the actual URL including your added data. Use that URL on your web page to link to the map.
Congratulations! You've just created your first Google Maps Mashup!
BTW, This is an excellent way to share placemarks with someone who, for some strange reason, does not have Google Earth installed.