This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
You could try appending a parameter to the URL of the page that contains the applet, and then read that via "getDocumentBase" in the applet. I think that should return the full URL of the page, including the parameter.