A demo of h2pe is now available from the project's website: http://h2pe.sourceforge.net/demo.html
The demo features FCK editor, linked to the h2pe library via a java servlet.
Currently the demo only provides very limited functionality, but it will be updated on a weekly basis to reflect any new features added to h2pe.
The next feature, planned for next week, will be to add the preview button as an FCK editor plugin, and provide the ability to configure the plugin to select a URL for the servlet.