If you just start out learning and investigating JBoss jBPM, make sure to also look at nexusBPM. Thanks to Burr Sutter from JBoss we had a meeting of local jBPM users at the JBoss offices in Atlanta yesterday. Mathew Sandoz gave us a presentation of nexusBPM (An open-source project he is working on), which adds a couple of really nice features to the jBPM designer.
While jBPM is rather bare-bone out of the box, nexusBPM adds several new workflow components such as FTP, SQL and a Script component that allow you to execute Groovy, Jython and BeanShell code. Also, Mathew Sandoz and his team added drag-and-drop deployment of workflows (pretty slick) to their extended jBPM designer as well as scheduling capabilities using Quartz.
Well, last night and today I spent some time installing and evaluating it. While the installation process is relatively smooth (Quite detailed documentation), the required infrastructure is rather specific. As of version 1.1 nexusBPM requires JBoss 4.05, Java 5 and Postgres as its database.
All in all it is a great package!