Model based implementation
I've put up a newer, Wicket 1.4 based solution on a gist at github. Provides the same functionality - a component that displays a JFreeChart with tooltips and clickable entities. This solution uses models and thus allows the graph to be redrawn when the model data changes.
This page details a component that integrates a JFreeChart chart and wicket producing a clickable imagemap integrated with a wicket AjaxLink, and tooltips specified via the tooltip generator of the JFreeChart.
The major component used by simply constructing and adding to your parent panel is MappedChart: