You can find the full source code for this website in the Seam package in the directory /examples/wiki. It is licensed under the LGPL.
Yes, Seam provides excellent support for AJAX. First, Seam supports the ICEfaces and Ajax4JSF Ajax component libraries for JSF. If you prefer a more
remoting example application on how to use AJAX remoting to implement a chat room. Finally, Seam's concurrency model is designed especially for use with Ajax.