Don't worry! It's only stuff...

copy "js" dir from gwt-ext archive int project web folder
 
Main.gwt.xml
add
        <inherits name="com.gwtext.GwtExt"/>
 
 
welcomeGWT.html
add
        <link rel="stylesheet" type="text/css" href="js/ext/resources/css/ext-all.css" />
        <link id="theme" rel="stylesheet" type="text/css" href="js/ext/resources/css/xtheme-silverCherry.css"/>
        <script type="text/javascript" src="js/ext/adapter/yui/yui-utilities.js"></script>
        <script type="text/javascript" src="js/ext/adapter/yui/ext-yui-adapter.js"></script>
        <script type="text/javascript" src="js/ext/ext-all.js"></script>
        <script type="text/javascript" src="js/ext/ext-lang-tr.js"></script>
 
 
Properties > Libraries > [ Add JAR/Folder ]
gwtext.jar