Sun have stopped development on the Servlet Development Kit, and given over control of the reference implementation to the Apache Group. To use later versions of the Servlet and
JSP APIs you need to get one of the servers which implements them.
You can download the reference "Tomcat" server from
http://jakarta.apache.com/ . Many of us prefer to use other implementations - I use Resin, available free for development from
http://www.caucho.com/ , which seems easier to install, is usually faster than
Tomcat, and includes some useful XML/XSL functionality.