d = document
	imagesNum = 21
	if (d.images) {
	ovrImages = []; outImages = []
	for (i=1;i<=imagesNum;i++) {
	ovrImages[i] = new Image()
	ovrImages[i].src = 'img/nav_b_' + i + '.gif'
	outImages[i] = new Image()
	outImages[i].src = 'img/nav_a_' + i + '.gif'
	}
	}
	function roll(i, isOver) {
	if (d.images) {
	d.images['b' + i].src = isOver ? ovrImages[i].src : outImages[i].src
	}
	}