What libraries are available to write a SOAP client in Java version 1.4.2?
Most of the common ones were around then; you're likely to need to go to archived versions though, as that's several major revisions old now. Java 5 in particular added enough goodness that its features tended to be adopted.
The two major options are Apache Axis/Axis2 and the Sun Metro JAX-WS stack (included in J2EE 5 and J2SE 6).
However, Metro is Java 5 and newer only, as it uses annotations.
I'm a fan of Apache CXF. Here's a tutorial on the different ways to develop a web service client:
http://cwiki.apache.org/CXF20DOC/how-do-i-develop-a-client.html
Neither Metro nor CXF will work with Java 1.4.x, they both require Java5. I think the only options are Axis/Axis2 and XFire, but even Axis2 1.5 is going to be Java 5 only and XFire is pretty much replaced by CXF. Java 1.4 is pretty much a dead end for WebServices stacks.