Calling a web service via javascript

[truezplaya]

I've searched numerous places on the web and haven't been able to get my solution to work. I have set up an web service and all works perfectly. It a very simple one just one method that retruns hello world as a string

namespace MyWebApp
{
    /// <summary>
    /// Summary description for FirstSharePointWebService
    /// </summary>
    [WebService(Namespace = "MyWebApp", Name = "FirstSharePointWebService")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [System.ComponentModel.ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    [System.Web.Script.Services.ScriptService]
    public class FirstSharePointWebService : System.Web.Services.WebService
    {
        [ScriptMethod]
        [WebMethod]
        public string HelloWorld()
        {
            return "Hello World";
        }
    }

I have then created a web part in SharePoint. In this web part all i am doing is adding a literal control to the page which is an input button. I am also adding another literal control which places the javascript on the page.

this.Controls.Add(new LiteralControl("
<script language='javascript' type='text/javascript'>(function(){
alert(1);
service.useService('http://localhost:22222/12/TEMPLATE/LAYOUTS/AJAX/FirstSharePointWebService.asmx?WSDL','FirstSharePointWebService');
}());
function callService() {alert(2);
MyWebApp.FirstSharePointWebService.HelloWorld(callComplete, callError);
} 
function callComplete(result){alert(result);}
function callError(result){alert('ERROR');}
</script>"));
                    
this.Controls.Add(new LiteralControl("
<input type='button' id='pow' value='Get Name' onclick='callService();' />"));

When i click on the button i get the callError() output which indicates it's all hooked up happily enough but something is wrong in the callComplete method and i can't spot what!

I am guessing it can't find the MyWebApp.FirstS harePointWebSer vice but i'm not sure.

Any pointers tips trick would be massively appreciated. Cheers
Truez