Going over the Migrating to Wicket 1.3 page and looking at the API changes which affect the FilmFestival project:
Using a Filter: Change the assignment of ServletContext in the WebApplication subclasses. Change the web.xml listing.
IModel change: The FilmFestival's DetachableBlogEntryModel need to extend some other class as per the migration mapping due to AbstractReadOnlyDetachableModel having been removed. Note the method name changes.
Interesting bit on CompoundPropertyModel. The project uses CompoundPropertyModels to automatically bind data elements to their page counterparts. As the approach used is different, alteration should not be required.
Validation: The API for validation has been moved from package wicket.markup.html.form.validation to package org.apache.wicket.validation.
Repeaters: This API has been moved from extensions to the core, requiring only a Ctrl-Shift-O to relink the classes affected in the import section.
DatePicker: This component has been removed. Alternatives listed need to be used.
Custom resource loading: Would this allow the html files to be separated from their java counterparts? The instructions here does not seem to use it.
One of the new features in Wicket 1.3 is Enclosure. Which, as shown here and here, is a way of toggling markup visibility for components.