In order to actually run this applet, you will need the Java 2 plugin which is available from java.sun.com/products/plugin. If the plugin has already been installed, you should see a button Start SIPN editor... just below this text. You can start the editor by pushing this button. The editor will show up as a new window...
If you have granted read access permissions, you can load a sample Petri net into the tool and simulate it. Please make sure that you first download the file into the directory to which you have granted read access and that its local name has suffix xml. The user interface of the applet version of the statechart editor for selecting files is very simple due to general access restrictions imposed on applets. You have to type in the complete path to your downloaded file (sorry...). If you, furthermore, have granted write access, you can even save edited statecharts and load them again.
You can also find a report describing the SIPN approach using a drill simulator.
There is also a web page dedicated to this editor at the University of Kaiserslautern: Institute's home page (Please navigate to "Software Products -> SIPN-Editor")