Note that the date of the article you're looking at is April 2004, which is way too old to be of any use here. The Easy Struts plugin home page has listed it as being "under refactoring" for at least a couple of years. Even if the plugin were still around, it would be useless to you because it was for Struts 1, and you're developing in Struts 2, which is a completely different Framework.
If you downloaded the version of Eclipse 3.3 that's for Java EE developers, you already have everything you need to develop Struts 2 applications. To get started, just import the struts-blank-2.0.11.war file that comes with the Struts 2 download into your workspace.