function newImage(arg) {
	if (document.images) {
		rslt = new Image();
		rslt.src = arg;
		return rslt;
	}
}

function changeImages() {
	if (document.images && (preloadFlag == true)) {
		for (var i=0; i<changeImages.arguments.length; i+=2) {
			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
		}
	}
}

function preloadImages() {
	if (document.images) {
		timelineanicallout_on = newImage("img/timelineanicallout_on.gif");
		timelineanicallout_off = newImage("img/timelineanicallout_off.gif");
		pahintrocallout_on = newImage("img/pahintrocallout_on.gif");
		pahintrocallout_off = newImage("img/pahintrocallout_off.gif");	
		linkssidecallouts_on = newImage("img/linkssidecallouts_on.gif");
		linkssidecallouts_off = newImage("img/linkssidecallouts_off.gif");	
		studydesignsidecallouts_on = newImage("img/studydesignsidecallouts_on.gif");
		studydesignsidecallouts_off = newImage("img/studydesignsidecallouts_off.gif");	
		downloadcallout_on = newImage("img/downloadcallout_on.gif");
		downloadcallout_off = newImage("img/downloadcallout_off.gif");	
		preloadFlag = true;
	}
}

var preloadFlag = false;