if (document.images)
{
	var tnOff = new Image();
	tnOff.src = "../images/tn_off.gif";
	var tnOn = new Image();
	tnOn.src = "../images/tn_on.gif";
}

function chgTNImg(imgField, newImg)
{
	if (document.images)
	{
		document[imgField].src = eval(newImg + ".src");
	}
}