Sorry. I'm using Ubuntu Linux
I would suggest leaving webroot where it is and simply replacing the contents. This is easy to do from an ant script in a post-installation phase. Create the webapp you'd like to be root, and after removing the contents of the default jboss app, copy yours in.
add file jboss-web.xml to WEB-INF,
and file content :
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE jboss-web PUBLIC
"-//JBoss//DTD Web Application 2.4//EN"