the tutorial on this blog is out-of-date. Please, use the following reference: http://docs.jboss.org/tools/3.1.0.M2/en/jboss_portal_tools_ref_guide/html_single/index.html#installation
All Jboss Tools documentation you can find here: http://jboss.org/tools/docs.html
If you use JBoss Portal + JBoss AS bundle as mentioned in tutorial, then a portlet library should be there. Just one thing there: to configure the project classpath to include the library, you should select "Portlet Target Runtime Provider" on the JBoss Portlet Capabilities page while creating a project.
For details, see http://www.jboss.org/community/wiki/PortletFacetLibraries
The docs should be updated nevertheless, thanks for pointing to this.