To build this applet you will need:
All of the instructions to install and configure the tools are available on their respective websites.
To those versed in using Ant, compile the project via the build.xml as you would do for any other project. Use the makedistro (the default) to generate everything or jar to get a usable jar file. Post queries on the forum if you're having trouble.
The JDK (Java Development Kit) is available from the Sun Microsystems Java website. Instructions on installing, updating and configuring are available there.