<script language="javascript">

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 change(value)
{
  var elem = document.getElementById('type');
  
  var req = Inint_AJAX();

  req.onreadystatechange = function ()
  {
    if (req.readyState == 4) 
    {
      if (req.status == 200) 
      {
        var text = req.responseText.toString(); //retuen value
        
        elem.innerHTML = text;
      }
    }
  };

  req.open('GET', 'ajax.php?type=' + value, true); //make connection
  req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded;charset=cp1251'); // set Header
  req.send(null); //send value  
}

</script>

<select id="select" onChange="javascript:change(this.value);">
  <option></option>
  <option value="1">Тип 1</option>
  <option value="2">Тип 2</option>
  <option value="3">Тип 3</option>
</select>
<br>
<br>
<select id="type"></select>