WAS Sneak Preview & JVM > 1.3.1_08

I have installed (successfully) the WAS 6.3 sneak preview. However, I am developing a program that uses some classes that are new with Java 1.4.2. I can get these compiled OK with the sneak prview, but cannot execute them. (I have installed JVM 1.3.1_08).

Can install a new Eclipse version on top of the sneak preview? If so, do I need to install the JVM for 1.4.2? The 1.4.2 JDK?

I need some detailed installation instructions to get all this done. Can anyone help?