Download and some env configure
 1. download gwt version gwt-windows-1.4.60 from http://code.google.com/webtoolkit
 2. unzip gwt-windows-1.4.60.zip file
 3. set system env variable GWT_HOME to the path where you hold your gwt files
 4. add %GWT_HOME% to your env path

Google Code Home > Google Web Toolkit > Getting Started Guide , it's a good place to get start.
You could follow this guide and get a first impression of what GWT can do and how convenient it is.

Usage
projectCreator -eclipse MyProject
ApplicationCreator [-eclipse projectName] [-out dir] [-overwrite] [-ignore] className

Eclipse plugin

cypal.studio.for.gwt
 1. download from http://code.google.com/p/cypal-studio/ version: cypal.studio.for.gwt-RC2.zip
 2. install this eclipse plugin (install it by new local site or just copy files, it's up on you )
 
GWT Designer 

 1. download from http://www.instantiations.com/gwtdesigner/index.html
 2. during install you need to choose Eclipse base location and GWT_HOME location
 
 Study how to use this plugin,
Webdemos
http://www.instantiations.com/gwtdesigner/demos.html

GWT desinger document homePage
http://downloads.instantiations.com/DesignerDoc/integration/latest/docs/html/gwt/index.html

Tutorial: Creating a Login application
http://downloads.instantiations.com/DesignerDoc/integration/latest/docs/html/gwt/tutorial/tutorial_login.html