I just spoke with someone at an Apple store, who told me that the Tiger OS will initially ship with Java 1.4. However, a beta version of Java 1.5 will be available for download from the Apple Developer site on April 29.
I went to an Apple store, and here's what I found:
It will "probably be about a month" before new PowerBooks and iBooks ship with the Tiger OS installed. However, as of April 29, a disk for the new operating system will be included with new computers for the user to install.
With respect to Java, I got shuffled around to a few people, and the bottom line -- at least from the weekend staff -- is they don't know which version of Java will be included with the operating system. (But I prefer an honest "I don't know" to a guess.)