According to the Apple website Java6 has finally been released for Mac OSX 10.5. No further details were given about support for other operating systems.
This Java for Mac OS X 10.5 Update 1 adds Java SE 6 version 1.6.0_05 to your Mac. This update does not replace the existing installation of J2SE 5.0 or change the default version of Java.
This release does not change the default version of Java. This release is only for Mac OS X v10.5.2 and later, and should not be installed on earlier versions of Mac OS X. This release is for 64-bit Intel-based Macs only and cannot run on PowerPC-based or 32-bit Intel-based Macs.
Software developers can visit the Java Reference Library for information on this release's features."