Replacing Running Web Site

Install in subfolder called wordpress, then to go live, just delete the /wordpress part at the end of the Options->General Blog address (URL) and put this index.php in your webroot:

<?php
/* Short and sweet */
define('WP_USE_THEMES', true);
require('./wordpress/wp-blog-header.php');
?>

Even though the actual WordPress files reside in a sub-directory, an index.php file is in your webroot, and the Options->General admin page Blog address (URL) is changed so that WordPress acts as your main page. This particular setup is described at: http://codex.wordpress.org/Giving_WordPress_Its_Own_Directory