1) A 1.5 JDK, download and install from java.sun.com. (Do not install the JDK in "Program Files" even though it wants to.)
2) Set JAVA_HOME to where JDK was installed
1) Download and unzip the JBossAS 4.2.3.GA version (latest production release). Do not unzip into "Program Files" (I have mine at d:\opt\jboss\jboss-4.2.3.GA)
1) Open command prompt at JBossAS bin directory (that is d:\opt\jboss\jboss-4.2.3.GA\bin for me)
2) Enter: run
3) Open browser, enter URL: http://localhost:8080
Read the first chapter (free download) of the book JBoss in Action (http://www.manning.com/jamae), it repeats the above and shows how to deploy a simple app. The book is based on JBossAS 5 (which is still not production ready), but much of the first chapter still works correctly for 4.2.3 (if I recall correctly, the only difference is some reorganization of the directory structure).