window.onload = function() {
	//100 is time between updates in milliseconds
	setInterval(ScrollHomePageAnimation, 40);
}

function ScrollHomePageAnimation() {
	var obj = document.getElementById("homepage_animation");
	var pos;
	// pos = 0, must match CSS class, this is the starting position
	if (obj.style.backgroundPosition == "")
		pos = 50;
	else
		pos = parseInt(obj.style.backgroundPosition);
	// number of pixels to move by at a time
	pos = pos - 1;
	obj.style.backgroundPosition = pos + "px 0";
}