Tasik, welcome to the JBoss forums!
Here are some things that might help:
Change JBoss AS to use port 80 for HTTP: http://community.jboss.org/wiki/JBossOnPort80
(You can do that only is you are not running IIS or Apache - it would be using port 80)
Change your web app to use the root context: http://community.jboss.org/message/277786#277786
There are also ways of placing an index.html page or index.jsp page into the root folder and have it redirect to the desired page. Something like this for a JSP (similar things are available for HTML, but they cause a resend to the browser):
<jsp:forward page="abc/common/index.jsp" />