I was going to say the same thing. It is a FCS release: First Customer Shipment.
I am looking for the jvm source code and other things. src.zip contains almost all the JAVA runtime source code (java source code), however there are some reference implementations whose source code is not in src.zip (for instance the RI for jcp 114: http://www.jcp.org/en/jsr/detail?id=114 ).
The source code to JDK 5.0 was released today (11/05/2004). Note that you can access it via the Sun Community Source License (SCSL) or the new Java Research License (JRL). JRL should be a bit easier to read and understand is not nearly as long.
http://java.sun.com/j2se/1.5.0/source_license.html
Regards