This is an example of using the WMS server with the Google Maps API map widget. View the page source to see how it works.
The map below shows color-coded U.S. congressioanl districts. Change which layer is displayed by changing the calls to addLayer in the script in this page. This also demonstrates using click pop-ups.
Note that my own Google API Key is used in the example. You will have to get your own from Google if you want to copy this page to your own website.