Straight from the ADC site (a free online account is enough to gain access to the download): "Java SE 6 Developer Preview 8 is an implementation of Sun's Java SE 6 for Mac OS X v10.5.1 and later. This Preview includes Java SE 6 version 1.6.0_01. This Developer Preview does not change the default version of Java. This release is only for Mac OS X v10.5.1 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."