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 really didn't give us much information to go off of, like what kind of server you have. If you are running a web container with servlets (notice that I'm still not sure), the common solution is to use MultipartRequest/MultipartParser or FileUpload on the server side and a multipart form or HttpClient on the client side.