The 57MB Java for Mac OS X 10.5 Update 1 release is intended for users running OS X 10.5.2 or later on 64-bit Intel-based Macs. Release notes from Apple say that the update can't run on PowerPC-based or 32-bit Intel-based Macs.
Java SE 6 was first released in 2006, and added a number of useful features for programmers who code in Java. However, when Leopard shipped last fall, it came out without Java SE 6 support, forcing programmers to either code for older Java releases on all platforms, or build a non-Java SE 6 version of their code just for the Mac. Apple had posted a developer preview of Java SE 6 for Leopard in December.
This story, "Apple Adds Support for Java SE 6 to Leopard" was originally published by Macworld.