function Inint_AJAX() {
   try { return new ActiveXObject("Msxml2.XMLHTTP");  } catch(e) {} //IE
   try { return new ActiveXObject("Microsoft.XMLHTTP"); } catch(e) {} //IE
   try { return new XMLHttpRequest();          } catch(e) {} //Native Javascript
   // alert("XMLHttpRequest not supported");
   return null;
};

function dochange(obj) {

zip =obj.value
nm="county";
nm2="tmout";

val="zip="+zip

 var req = Inint_AJAX();  		 
     req.onreadystatechange = function () {
     
          if (req.readyState==4) 
          {
               if (req.status==200) 
               {
			
			document.getElementById(nm).value=req.responseText;
			document.getElementById(nm2).value="OK";
			
		}
               

          }

     };
     
     req.open("GET", "zip.php?"+val); //make connection
     req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;charset=iso-8859-1"); // set Header
     req.send(null); //send value
 
 
}