I suggest taking a look at [5 Tips for using jQuery with WordPress][1].  Among other things, it shows the code necessary to load jQuery from Google's library:

    function my_init() {
    	if (!is_admin()) {
    		// comment out the next two lines to load the local copy of jQuery
    		wp_deregister_script('jquery');
    		wp_register_script('jquery', 'http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js', false, '1.3.2');
    		wp_enqueue_script('jquery');
    	}
    }
    add_action('init', 'my_init');


You could also check out the [Use Google Libraries][2] plugin.


  [1]: http://www.ericmmartin.com/5-tips-for-using-jquery-with-wordpress
  [2]: http://wordpress.org/extend/plugins/use-google-libraries/