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.
A URL (Uniform Resource Locator) is a kind of address while a URN (Uniform Resource Name) is just a name without any hint about the actual location of the particular resource. For example, "http://www.google.com" is a URL while "urn:google" is a URN.