This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
On the client side you are looking at creating a URLConnection to the URL of a servlet, opening a stream, writing a request and reading a response stream. URLConnection is in the java.net package, part of the standard SDK library. The alternative would be to open a socket, but URLConnection is simpler. On the server side you are obviously talking about a class derived from HttpServlet. You can download Tomcat and get the API docs. Bill