From NeOn Wiki

Jun 30 2008. The current release of the NeOn Toolkit v.1.1 has no built-in feature to model OWL ontologies. This feature is work in progress. If you want to try it out you can test it nevertheless. In order to do so we set up an easy way to install this feature from within the NeOn Toolkit via the software update feature. Just go to Help > Software Update > Find and Install > Search for new Features to Install. Here you will find the NeOn Toolkit update site which contains the recent version of the OWL modeling support.