Usually you would place the distribution in /usr/local or /opt depending on your preference. So it would be /usr/local/jboss3.0.8.
JBOSS_HOME is not a variable you need to create or use.
chown -R untz:users /usr/local/jboss3.0.8
As long as you understand the ownership and security of this configuration.
You will need JAVA_HOME defined but you can modify this in /usr/local/jboss3.0.8/bin/run.conf or otherwise define it directly in /usr/local/jboss3.0.8/bin/run.sh. Again, it depends on your preference.