var imgObjSupport = false;
if (document.images) {imgObjSupport = true;} else {imgObjSupport = false;}
if (imgObjSupport) {

but_off = new Image();
but_off.src = "/pic/but.jpg";
but_on = new Image();
but_on.src = "/pic/but2.jpg";

}
function roll_on(imgName) {
	if (imgObjSupport) {
		imgOn = but_on.src;
		document [imgName].src = imgOn;
	}
}

function roll_off(imgName) {
	if (imgObjSupport) {
		imgOff = but_off.src;
		document [imgName].src = imgOff;
	}
}