buttonImg = new Array();

for(i = 0;i <= 7;i++){
	buttonImg[i] = new Image();
	buttonImg[i].src = "img/button_" + i + "_on.gif";
}

function imageOn(n){
	document.images['btn' + n].src = buttonImg[n].src;
}

function imageOff(n){
	document.images['btn' + n].src = "img/button_" + n + "_off.gif";
}