Go grab it at ADC site!
Looks like there's only an Intel version at the moment, PPC not implemented yet.
BTW - Java 1.3.1 was not ported to Intel - Intel Macs ship with PPC version and performance is poor... who cares - future is Java 6!
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UPDATE: I just ran a few tests, most new Desktop Integration features seem to work fine - System Tray, launching default application, mail client. Default Web browser didn't work as expected - yet.
These features may not be that important for mostly full-screen games, however we can all use some speed, right? Scimark2 results follow:
(same jar, same Intel HW - 1.83 GHz Core Duo, 1 GB RAM, OS 10.4.6)
1.3.1_16 - 001.47 (no typo, this is PPC Java on Intel!)
1.4.2_09 - 210.87 (that's more like it!)
1.5.0_06 - 251.96 (better!)
1.6.0-dp - 298.92 (is this cool or what?)