Jan Bot's CytoscapeRPC plugin (with a few additions of my own); includes apache xmlrpc libraries: RPC.jar
Copy this into your Cytoscape/plugins directory, where it will be discovered & loaded the next time you start Cytoscape.
Duncan Lang's XMLRPC R package, slighly modified by me: XMLRPC_0.2-13.tar.gz
once downloaded: R CMD INSTALL XMLRPC_0.2-13.tar.gz