Using GXmlHttp and Webservices

Question

I'm trying to use GXmlHttp in the Google Maps API to call a Webservice of mine (myService.asmx?op=myMethod) and am not having luck. Is there a way to call this web method using this object? Some sample code:

var request = GXmlHttp.create();
request.open("POST", "http://myDomain/MyServicee.asmx?op=MyMethod", true);

Nothing comes back. IT gets to readystate 4 but the method is never called. Any help is greatly appreciated!