Another example of the Bascom-AVR W5100 library. Hardware, Arduino Mega with a W5100 ethernetshield and a DHT11 temperature/humidity sensor.
It will wait for a request from Google Earth and when contacted, it will send a KML-file. Now temperature/humidty is send, but that can be any value like alarms, values etc.
The way you make a network link in Google Earth.
And with a second socket on the W5100 you can even switch things on/off with an telnet-session