window.onresize = doSize;

function doSize()
{	
	var newWidth = document.body.clientWidth;
	var newLeft;
	var baseWidth = 1024;

	if (newWidth <= baseWidth) 
	{
		newLeft	= 0;
	}
	else
	{
		newLeft	= (newWidth - baseWidth) / 2;
	}
	
	newLeft += "px";
	
	var elm = document.getElementById("mainDiv");
	
	elm.style.left = newLeft;
	elm.style.visibility = "visible";
}