function getWindowHeight() 
{
	var windowHeight = 0;
	if (typeof(window.innerHeight) == 'number') 
	{
		windowHeight = window.innerHeight;
	}
	else 
	{
		if (document.documentElement && document.documentElement.clientHeight) 
		{
			windowHeight = document.documentElement.clientHeight;
		}
		else 
		{
			if (document.body && document.body.clientHeight) 
			{
				windowHeight = document.body.clientHeight;
			}
		}
	}
	return windowHeight;
}

function VerticallyCentreBodyDiv()
{
	VerticallyCentreContent("BodyDiv");
}

function VerticallyCentreContent(id) 
{
	if (document.getElementById) 
	{		
		var windowHeight = getWindowHeight();
		if (windowHeight > 0) 
		{
			
			var contentElement = document.getElementById(id);
			var contentHeight = contentElement.offsetHeight;
			if (windowHeight - contentHeight > 0) 
			{
				contentElement.style.position = 'relative';
				contentElement.style.top = ((windowHeight / 2) - (contentHeight / 2)) + 'px';
			}
			else 
			{
				contentElement.style.position = 'static';
			}
		}
	}
}

window.onresize = VerticallyCentreBodyDiv;