According to the Java Posse podcast, the “Java 5 release 4” for OS X 10.4 is available for download (possible only from their developer site?).
This release is based on the corresponding 1.5.0_06 Sun release, as opposed to 1.5.0_04, as you might expect by the naming scheme. This new Apple release, when installed, makes Java 5 the default JVM (whereas before this release, 1.4 was the default, even if 5.0 was installed). Unfortunately, Apple will apparently not be releasing Java 5 for anything older than OS X 10.4, by the way.
And there you go.