Assumming noone change the defaults, you can access it via http://localhost:8080
You can change the port in jboss-5.1.0.GA\server\default\deploy\jbossweb.sar\server.xml (same instructions as for Tomcat)
You can change the hostname by using the -b run option, see also the first netry here: https://community.jboss.org/wiki/JBoss42FAQ