var backgroundHeight = 900;

$(document).ready(function(){
	$(window).bind('resize', function() {
		resizeHandler();
	});
	resizeHandler();
});

function resizeHandler()
{	
	var winSize = getWindowSize();
	var winH = winSize[1];

	var body = document.body;
	var top = (backgroundHeight > winH) ? 0 : winH - backgroundHeight;
	$("body").css("backgroundPosition",  "50% " + top + "px");
}

function getWindowSize()
{
	var myWidth = 0, myHeight = 0;
	if( typeof( window.innerWidth ) == 'number' ) {
		//Non-IE
		myWidth = window.innerWidth;
		myHeight = window.innerHeight;
	} else if( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ) {
		//IE 6+ in 'standards compliant mode'
		myWidth = document.documentElement.clientWidth;
		myHeight = document.documentElement.clientHeight;
	} else if( document.body && ( document.body.clientWidth || document.body.clientHeight ) ) {
		//IE 4 compatible
		myWidth = document.body.clientWidth;
		myHeight = document.body.clientHeight;
	}
	
	return [myWidth, myHeight];
}