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(src, val) {
var req = Inint_AJAX();
req.onreadystatechange = function () {
 if (req.readyState==4) {
      if (req.status==200) {
           document.getElementById(src).innerHTML=req.responseText; //retuen value
      }
 }
};
req.open("GET", "src_category.php?data="+src+"&val="+val); //make connection
req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=windows-1250');
req.send(null); //send value
}

window.onLoad=dochange('categories', 2);         // value in first dropdown