You should check the Drools Guvnor documentation. Though installing it is pretty easy, usually just dropping the war in the AS. If you use the jbpm-installer, it automatically downloads and installs guvnor for you.
Note that Guvnor integration was not yet available in jBPM 5.0 CR1, it is however currently available in the latest snapshot. I'll be making a blog entry and screencast about it in the next few days, so keep your eyes on the blog ;)
Kris