C# using VS2010
WSDL to use, added as a service reference not web reference.
Initialisation
                            //The client object
cb.Clearbooks_Service_ApiPortClient client = new cb.Clearbooks_Service_ApiPortClient();
 
//The apiKey object
cb.authenticate auth = new cb.authenticate();
auth.apiKey = "YOUR_API_KEY";
                            
                        