function preLoadImages() {
}

function changeOn(level, imageName, fileType) {
    if (document.images) {
		document.images[imageName].src = level + "images/" + imageName + "_on." + fileType;
	}
}

function changeOff(level, imageName, fileType) {
    if (document.images) {
		document.images[imageName].src = level + "images/" + imageName + "_off." + fileType;
	}
}