Automatically include jQuery to your blog’s theme by entering the following script in your theme’s functions.php page:

if (!is_admin()) {
wp_deregister_script('jquery');
wp_register_script('jquery', ("http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"), false, '1.3.2');
wp_enqueue_script('jquery');
};

Not only do you not have to worry about including it in the header.php file of your theme, but it will always pull the most up-to-date version from Google’s servers.