Storage media
For installation media on an http server the address should resemble "http://servername.example.com/pub/dist/rhel5" where the actual source on your local host is /var/www/html/pub/dist/rhel5.
For installation media on an ftp server the address should resemble "ftp://servername.exampe.com/dist/rhel5", where the actual source on your local host is /var/ftp/pub/dist/rhel5.
For installation media on an NFS server the address should resemble "nfs:servername.example.com:/dist/rhel5". The actual location depends on your NFS share. Use the system-config-nfs command to configure NFS to share media.
For more information on configuring these network services read the relevant sections of your Red Hat Enterprise Linux Deployment Guide in the System->Documentation menu.