var XHR1 = new xHttpRequest();
var XHR2 = new xHttpRequest();
var XHR3 = new xHttpRequest();
var XHR4 = new xHttpRequest();

function getXHR()
{
  if (XHR1.busy)
  {
    if (XHR2.busy)
    {
      return null;
    } else return XHR2;
  } else return XHR1;
}

// xHttpRequest, Copyright 2006-2007 Michael Foster (Cross-Browser.com)
// Part of X, a Cross-Browser Javascript Library, Distributed under the terms of the GNU LGPL

function xHttpRequest() // object prototype
{
  // Private Properties
  var _i = this; // instance object
  var _r = null; // XMLHttpRequest object
  var _t = null; // timer
  var _f = null; // callback function
  var _x = false; // XML response pending
  var _o = null; // user data object passed to _f
  // Public Properties
  _i.OK = 0;
  _i.NOXMLOBJ = 1;
  _i.REQERR = 2;
  _i.TIMEOUT = 4;
  _i.RSPERR = 8;
  _i.NOXMLCT = 16;
  _i.status = _i.OK;
  _i.busy = false;
  // Private Event Listeners
  function _oc() // onReadyStateChange
    {
      if (_r.readyState == 4) {
        if (_t) { clearTimeout(_t); }
        if (_r.status != 200) _i.status = _i.RSPERR;
        if (_x) {
          var ct = _r.getResponseHeader('Content-Type');
          if (ct && ct.indexOf('xml') == -1) { _i.status |= _i.NOXMLCT; }
        }
        if (_f) _f(_r, _i.status, _o);
        _i.busy = false;
      }
    }
  function _ot() // onTimeout
    {
      _r.onreadystatechange = function(){};
      _r.abort();
      _i.status |= _i.TIMEOUT;
      if (_f) _f(_r, _i.status, _o);
      _i.busy = false;
    }
  // Public Method
  this.send = function(m, u, d, t, r, x, o, f)
    {
      if (!_r || _i.busy) { return false; }
      m = m.toUpperCase();
      if (m != 'POST') {
        if (d) {
          d = '?' + d;
          if (r) { d += '&' + r + '=' + Math.round(10000*Math.random()); }
        }
        else { d = ''; }
      }
      _x = x;
      _o = o;
      _f = f;
      _i.busy = true;
      _i.status = _i.OK;
      if (t) { _t = setTimeout(_ot, t); }
      try {
        if (m == 'GET') {
          _r.open(m, u + d, true);
          d = null;
          _r.setRequestHeader('Cache-Control', 'no-cache');
          var ct = 'text/' + (x ? 'xml':'plain');
          if (_r.overrideMimeType) {_r.overrideMimeType(ct);}
          _r.setRequestHeader('Content-Type', ct);
        }
        else if (m == 'POST') {
          _r.open(m, u, true);
          _r.setRequestHeader('Method', 'POST ' + u + ' HTTP/1.1');
          _r.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        }
        else {
          _r.open(m, u + d, true);
          d = null;
        }
        _r.onreadystatechange = _oc;
        _r.send(d);
      }
      catch(e) {
        if (_t) { clearTimeout(_t); }
        _f = null;
        _i.busy = false;
        _i.status = _i.REQERR;
        _i.error = e;
        return false;
      }
      return true;
    };
  // Constructor Code
  try { _r = new XMLHttpRequest(); }
  catch (e) { try { _r = new ActiveXObject('Msxml2.XMLHTTP'); }
  catch (e) { try { _r = new ActiveXObject('Microsoft.XMLHTTP'); }
  catch (e) { _r = null; }}}
  if (!_r) { _i.status = _i.NOXMLOBJ; }
}