var ajaxpageclass=new Object()
ajaxpageclass.loadstatustext="<img src='images/loading.gif' /> <span style='color:gray;'>Загружается...</span>" 
ajaxpageclass.ajaxbustcache=false
function mypageload(pageurl, divId){
	var page_request = false
	var bustcacheparameter=""
	if (window.XMLHttpRequest) // Mozilla, IE7, Safari
		page_request = new XMLHttpRequest()
	else if (window.ActiveXObject){ // IE6 or below
		try {
		page_request = new ActiveXObject("Msxml2.XMLHTTP")

		}
		catch (e){
			try{
			page_request = new ActiveXObject("Microsoft.XMLHTTP")
			}
			catch (e){}
		}
	}
	else
		return false
	page_request.onreadystatechange=function(){ajaxpageclass.loadpage(page_request, divId)}
	if (this.ajaxbustcache) 
		bustcacheparameter=(pageurl.indexOf("?")!=-1)? "&"+new Date().getTime() : "?"+new Date().getTime()
	page_request.open('GET', pageurl+bustcacheparameter, true)
	page_request.send(null)
}
ajaxpageclass.loadpage=function(page_request, divId){
	document.getElementById(divId).innerHTML=this.loadstatustext
	if (page_request.readyState == 4 && (page_request.status==200 || window.location.href.indexOf("http")==-1)){
		document.getElementById(divId).innerHTML=page_request.responseText
	}
}

<a href="how_order.htm" target="_blank" onclick="if (document.getElementById('my_content').innerHTML==''){mypageload('how_order.htm?' + Date(),'my_content');}else{document.getElementById('my_content').innerHTML='';document.getElementById('my_content').innerText='';} return false">
<strong> как заказать</strong></a>