You don't need anything. The JBoss IDE plugins can help you (re)deploy your application but you can go without.
A Portlet application is not much different that a Web Application, you need to use the portlet-api-lib.jar that is in included in JBoss Portal.
You also need to package your application with the correct descriptors (at least portlet.xml) and deploy the result war file by copying it to the jboss-4.0.4.GA/server/default/deploy directory
You should read the portlet specification and the Portal guides.