Override a WordPress 404 with a specific template

gistfile1.php

<?php

/**
 * Override a 404
 *
 * @param	string	$template	If passed, this template will be included and
 * 					the request will be terminated if the inclusion
 * 					was successful
 * @param	string	$type		If not a 404, what type of request should this be
 * 					flagged as? Must correspond to one of the
 * @return	void
 */
function pilau_override_404( $template = null, $type = 'page' ) {
	global $wp_query;

	// Change type of query
	$wp_query->is_404 = false;
	$type_property = "is_$type";
	if ( property_exists( $wp_query, $type_property ) )
		$wp_query->$type_property = true;

	// Make sure HTTP status is good
	status_header( '200' );

	// Load template?
	if ( $template ) {
		$template_found = locate_template( $template, true );
		if ( $template_found )
			exit;
	}

}