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 JDK and JRE downloads are different for different operating systems, eg Windows, Linux. And there may be different versions for different chips, but most people nowadays use an i386, which works on Pentium, most AMDs (I think, not sure), etc.