What does this Java update do? It adds support for Java SE 6 version 1.6.0_05, though only for 64-bit Intel Macs. PowerPC and 32-bit Intel Macs are not invited to this update party. You should note that this update doesn't replace the default install of Java on your Mac, it merely adds support for SE 6.
This update requires OS x 10.5.2 or higher.