function ajax_call(url, param, ret_func)
{
	var AJ;
	var activexmodes=["Msxml2.XMLHTTP", "Microsoft.XMLHTTP"]; //activeX versions to check for in IE
	if (window.ActiveXObject)
	{ //Test for support for ActiveXObject in IE first (as XMLHttpRequest in IE7 is broken)
		for (var i=0; i < activexmodes.length; i++)
		{
			try
			{
				AJ = new ActiveXObject(activexmodes[i])
			}
			catch(e)
			{
				//suppress error
			}
		}
	}
	else if (window.XMLHttpRequest) // if Mozilla, Safari etc
		AJ = new XMLHttpRequest();
	else
		return false;

	AJ.open("POST", url, true);
	AJ.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
	AJ.setRequestHeader("Content-length", param.length);
	AJ.setRequestHeader("charset", "iso-8859-1");
	AJ.setRequestHeader("Connection", "close");
	AJ.onreadystatechange = ret_func;
	//AJ.send(param); // debe estar comentada pues produce una llamada a la funcion en una variable que aun no esta declarada
	
	return AJ;
}