You just need a recent ANT release installed and a JDK 1.3.1 or higher. It may work with a JDK 1.3.0 but I haven't tried. A few people have had a problem with some versions of JDK 1.3.0 and JDK 1.3.1.
In the build directory of the source, there is a build.sh. If you run that it will build a JBoss distribution in the output subdirectory. Make sure that JAVA_HOME and ANT_HOME are correctly configured for your environment.