Unfortunately you cannot publish your web site to a cPanel server directly using iWeb. What you need to do to publish a web site created with iWeb to a cPanel server is publish the web site from iWeb to a folder/directory on your local disk drive and then use an FTP client like CyberDuck to FTP the site to the cPanel server. Remember that all of the site files must be put into the "public_html" folder/directory.