function getXmlHttp()
{
   var xmlHttp;

   try
   {
     // Firefox, Opera 8.0+, Safari
     xmlHttp = new XMLHttpRequest();
   }
   catch (e)
   {
     try 
     {
       // Internet Explorer
       xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
     }
     catch (e)
     {
       try
       {
         xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
       }
       catch (e)
       {
         xmlHttp = null;
       }
     }
   }

   return xmlHttp;
}