The JRE is provided in two different packages for Windows,Linux and Solaris from Sun. One is the JRE-only and the other is the SDK which contains the JRE. For Mac OS X, the full SDK,with the JRE included, is provided in every Mac OS X installation in /System/Library/Frameworks/JavaVM.framework/Versions/1.5/ and is updated from Apple's Software Update when Apple has prepared a new version/patch. So basically you DON'T install Java in a Mac, Apple does this for u.