NN4 = (navigator.appVersion.charAt(0)>=4 && (navigator.appName).indexOf("Netscape") != -1);
IE4 = (navigator.appVersion.charAt(0)>=4 && (navigator.appVersion).indexOf("MSIE") != -1);

if ((NN4 == true) || (IE4 == true)){
	var onimg = new Array();
	var ofimg = new Array();
	var sonimg = new Array();
	var sofimg = new Array();
	
	for(i=1;i<6;i++){
		onimg[i] = new Image();
		onimg[i].src = "image/top_m" + i + "on.gif";
	}

	for(i=1;i<6;i++){
		ofimg[i] = new Image();
		ofimg[i].src = "image/top_m" + i + ".gif";
	}
	
	for(i=1;i<7;i++){
		sonimg[i] = new Image();
		sonimg[i].src = "image/sub_m" + i + "on.gif";
	}

	for(i=1;i<7;i++){
		sofimg[i] = new Image();
		sofimg[i].src = "image/sub_m" + i + ".gif";
	}
}
function bt_on(nam1,num1) {
	document.images[nam1].src = onimg[num1].src;
}

function bt_off(nam1,num1) {
 	document.images[nam1].src = ofimg[num1].src;
}

function sbt_on(nam1,num1) {
	document.images[nam1].src = sonimg[num1].src;
}

function sbt_off(nam1,num1) {
 	document.images[nam1].src = sofimg[num1].src;
}