Welcome to the JavaRanch.
Where did you find this example? It's sure looks wrong. The struts.xml file should be under the WEB-INF directory. Your helloworld.class file should be under classes, not lib. The path is case-sensitive, so I think CLASSES is wrong as well.
If you want a good example, several come with the Struts distribution, including a blank application that you can extend with your own code.