Hi Pedro,
Try to do what it's explain in this tutorial : http://docs.jboss.org/jbpm/v5.4/userguide/ch.installer.html#d0e481
You can also look at this video to understand how it's work in eclipse : http://people.redhat.com/kverlaen/jbpm-installer-eclipse-5.2.swf
BR,
Nicolas Louis.