You want to install Google Plugin (e.g Google Web Toolkit aka GWT and Google App Engine Java SDK) in Eclipse.
In this tutorial, I will show you how to install Google Plugin for Eclipse on Eclipse 3.4 aka Ganymede.
Here are the steps:
Run Eclipse and go to Help > Software Updates…
Click Add Site… and paste this URL in the Location field then click OK
Eclipse will automatically retrieve and detect the available plugins. Then you will see the Plugins and the SDKs.
Select which plugins you want to install then click Install… button. Wait for some minutes to let Eclipse install the plugins.
After the installation is successful, Eclipse need to be restarted for the change to take effect.