var xmlHttp

//Funcion para crear un objeto ajax
function GetXmlHttpObject(handler)
{ 
	var objXmlHttp=null;
	
	try
	{
		if (navigator.appVersion.indexOf("MSIE 7")>=0)
			throw(new Exception("IE7"));

		objXmlHttp=new XMLHttpRequest();
		objXmlHttp.onload=handler;
		objXmlHttp.onerror=handler ;
		return objXmlHttp;
	}
	catch(ex)
	{
		if (navigator.userAgent.indexOf("MSIE")>=0)
		{ 
			var strName="Msxml2.XMLHTTP";
			if (navigator.appVersion.indexOf("MSIE 5.5")>=0)
			{
				strName="Microsoft.XMLHTTP";
			} 
			try
			{ 
				objXmlHttp=new ActiveXObject(strName);
				objXmlHttp.onreadystatechange=handler ;
				return objXmlHttp;
			} 
			catch(e)
			{ 
				alert("Error. Scripting for ActiveX might be disabled") ;
				return ;
			} 
		}
		else
		{
			alert(ex);
		}
	}
}

// global request and XML document objects
var req;

// retrieve XML document (reusable generic function);
// parameter is URL string (relative or complete) to
// an .xml file whose Content-Type is a valid XML
// type, such as text/xml; XML source must be from
// same domain as HTML file
function loadXMLDoc(url) {	
    // branch for native XMLHttpRequest object
    if (window.XMLHttpRequest) {
        req = new XMLHttpRequest();
        req.onreadystatechange = processReqChange;
        req.open("GET", url, true);
        req.send(null);
    // branch for IE/Windows ActiveX version
    } else if (window.ActiveXObject) {
        //isIE = true;
        req = new ActiveXObject("Microsoft.XMLHTTP");
        if (req) {
            req.onreadystatechange = processReqChange;
            req.open("GET", url, true);
            req.send();
        }
    }
}

// handle onreadystatechange event of req object
function processReqChange(){
	// only if req shows "complete"
	if (req.readyState == 4) {
		// only if "OK"
		//alert(req.status)
		try
		{
			if (req.status == 200) 
			{
				// ...processing statements go here...
				response  = req.responseXML.documentElement;
				method = response.getElementsByTagName('method')[0].firstChild.data;
				
				var start = req.responseText.indexOf('<result>') + 8
				var stop = req.responseText.indexOf('</result>')
				result = req.responseText.substring(start,stop);

				eval(method + '(\'\', result)');
			} 
			else 
			{
				alert("Hubo un problema al traer los datos XML:\n" + req.statusText);
			}
		}		
		catch(ex)
		{
			alert(ex);
		}
	}
}