Does this not help?
To connect to a Web service on another machine with a different user name and password, you must create the proper credentials. The following code is an example of how to do this using an existing itemMS proxy class object.
CopyC#
string targetServer = "computer5";
string domain = "WORKGROUP";
string username = args[0];
string password = args[1];
itemMS.Url = string.Format( "http://{0}/Altiris/ASDK.NS/ItemManagementService.asmx", targetServer );
CredentialCache cache = new CredentialCache();
cache.Add( new Uri(itemMS.Url), "Negotiate", new NetworkCredential( username, password, domain ) );
itemMS.Credentials = cache;