function makeRequest(){    
  var http_request = false;
  if(window.XMLHttpRequest){  // Mozilla, Safari,...
    http_request = new XMLHttpRequest();
    return http_request;
  }else if(window.ActiveXObject) { // IE
    try {
      http_request = new ActiveXObject("Msxml2.XMLHTTP");
      return http_request;
    } catch (e) {
      try {
        return http_request = new ActiveXObject("Microsoft.XMLHTTP");
      } catch (e) {}
    }
  }
}

function GoAjax(url,SendString,FunctionName){
  http_request =  makeRequest();

  if(!http_request){
    alert('Giving up: Cannot create an XMLHTTP instance');
    return false;
  }
  
  if(window.ActiveXObject){
    http_request.onreadystatechange = function() { 
      if(http_request.readyState == 4) {
        eval(FunctionName+"();");
      }
    }
  }else{
    http_request.onload = eval(FunctionName);
  }
  
  http_request.open('POST', url, true);
  http_request.setRequestHeader("If-Modified-Since","0");
  http_request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
  http_request.send(SendString);
}