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 2of2 in the name of the file you've downloaded means that this is the second file from the set of two files. You need to download the first file as well. I believe the first one will contain the installer.