I just saw that Java for Mac OS X 10.4, Release 6 is now available from Apple. At first I thought this was "Java 6", but it's not. As you see from the release notes shown below it really updates either Java 5 or Java 1.4:
"Java for Mac OS X 10.4, Release 6 delivers improved reliability and compatibility for Java 2 Platform Standard Edition 5.0 and Java 1.4 on Mac OS X 10.4.10 and later. This release updates J2SE 5.0 to version 1.5.0_13 and Java 1.4 to version 1.4.2_16."
I haven't seen anything about this on Apple's website yet, but found it this morning when running the Software Update program.