function switch_ads(ct,dt,ad) {
	// ct = chart type
	// dt = date period
	// ad = active div - the box we're modifying
	
	var req;
	var e;
	var url;
	
	e = document.getElementById(ad); // get the email input field
	url = "/ajax_charts.cfm?ct=" + ct + "&dt=" + dt + "&random=" + Date();// create the url
	
	e.style.height='500px';
	
	// Check whether to use IE http request object
    if (window.XMLHttpRequest) {
		req = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
    	req = new ActiveXObject("Microsoft.XMLHTTP");
    isIE=true;
    }
	
	req.open("GET", url, true);  // open url 
	req.onreadystatechange = function() {
	
		e.innerHTML = 'Loading, please wait...';
		
	if (req.readyState == 4) {  // only do stuff when results have been retrieved
		e.innerHTML=req.responseText;
		e.style.height = '';
	}
} 
	req.send(null); // clear the object
	
	return;
}