Some example code for using XML RPC. Originally from: http://jumping-duck.com/tutorial/using-xml-rpc-in-wordpress/

xml-rpc-wordpress-example.php

<?php

// include wordpress so that we have access to some of the prebuilt functionality
include_once( $_SERVER['DOCUMENT_ROOT'] . '/wp-load.php' );

// include helper classes
include_once( $_SERVER['DOCUMENT_ROOT'] . '/wp-includes/class-IXR.php' );
include_once( $_SERVER['DOCUMENT_ROOT'] . '/wp-includes/class-wp-http-ixr-client.php' );

// create new XMLRPC Client
$client = new WP_HTTP_IXR_CLIENT( 'http://www.mydomain.com/xmlrpc.php' );

// say hello!
$hello = $client->query( 'demo.sayHello', array() );

// add two numbers together
$addition = $client->query( 'demo.addTwoNumbers', array( 55, 17 ) );