if (document.images) {
var nav_buspt = new Image()
nav_buspt.src = 'img/top_main_bt_buspt.jpg';
var nav_buspt_b = new Image()
nav_buspt_b.src = 'img/top_main_bt_buspt_ov.jpg';

var nav_ir = new Image()
nav_ir.src = 'img/top_main_bt_ir.jpg';
var nav_ir_b = new Image()
nav_ir_b.src = 'img/top_main_bt_ir_ov.jpg';

var nav_sup = new Image()
nav_sup.src = 'img/top_main_bt_sup.jpg';
var nav_sup_b = new Image()
nav_sup_b.src = 'img/top_main_bt_sup_ov.jpg';
}

function act(imgName) {
	if(document.getElementById(imgName))
	document.getElementById(imgName).src = eval(imgName + '_b.src');
}

function inact(imgName) {
	if(document.getElementById(imgName))
	document.getElementById(imgName).src = eval(imgName + '.src');
}