if (document.images) {
	btn_01_on = new Image();
	btn_01_on.src = "images/btn_01_on.png";
	btn_01_off = new Image();
	btn_01_off.src = "images/btn_01_off.png";
	btn_02_on = new Image();
	btn_02_on.src = "images/btn_02_on.png";
	btn_02_off = new Image();
	btn_02_off.src = "images/btn_02_off.png";
	btn_03_on = new Image();
	btn_03_on.src = "images/btn_03_on.png";
	btn_03_off = new Image();
	btn_03_off.src = "images/btn_03_off.png";
	btn_04_on = new Image();
	btn_04_on.src = "images/btn_04_on.png";
	btn_04_off = new Image();
	btn_04_off.src = "images/btn_04_off.png";
}

function turnon(imageName) {
	if (document.images) {
		document[imageName].src = eval(imageName + "_on.src");
	}
}

function turnoff(imageName) {
	if (document.images) {
		document[imageName].src = eval(imageName + "_off.src");
	}
}