function viewport(){
	var viewportwidth;
	var viewportheight;
	var containerHeight = 555;
	var containerTopMargin;
	
	// 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
	}
	
	containerTopMargin=(viewportheight/2)-(containerHeight/2);
	
	if(containerTopMargin<0){
		containerTopMargin=0;
	}
	
	document.getElementById('container').style.marginTop=containerTopMargin+'px';
}