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.
The HttpClient library can help greatly in implementing file upload over HTTP, and the FileUpload library can handle the server part (assuming that the server is a servlet engine). See http://faq.javaranch.com/java/FileUpload for detail.