Umm podrias usar include o require sin problemas ha pero deves de considerar q include y require para URLS solo funciona en PHP5.
asi podrias usar el codigo arriba q te dieron:
<?php
error_reporting(E_ALL);
/* We need the GET variables: */
extract($HTTP_GET_VARS);
/* Load PHP Weather */
require('http://www.instalaservicios.com/clima/phpweather.php');
/* Load utilities to make forms */
require('http://www.instalaservicios.com/clima/pw_utilities.php');
if (empty($language)) $language = 'es';
$weather = new phpweather();?>
require(PHPWEATHER_BASE_DIR . "/output/pw_text_$language.php");
require(PHPWEATHER_BASE_DIR . "/output/pw_images.php");
$type = 'pw_text_' . $language;
$text = new $type($weather);
$icons = new pw_images($weather);
echo '<p><img src="'.$icons->get_sky_image().'" /> ';
echo "<p>\n" . $text->print_pretty() . "</p>\n";
?>