function getViewportSize() {
	var viewportwidth;
	var viewportheight;
	// the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight
	if (typeof window.innerWidth != 'undefined') {
		viewportwidth = window.innerWidth;
		viewportheight = window.innerHeight;
	}
	// IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)
	else if (
		typeof document.documentElement != 'undefined' &&
		typeof document.documentElement.clientWidth != 'undefined' &&
		document.documentElement.clientWidth != 0
	) {
		viewportwidth = document.documentElement.clientWidth;
		viewportheight = document.documentElement.clientHeight;
	}
	// older versions of IE
	else {
		viewportwidth = document.getElementsByTagName('body')[0].clientWidth;
		viewportheight = document.getElementsByTagName('body')[0].clientHeight;
	}
	return {width:viewportwidth, height:viewportheight};
}