function setBtn(elt, icon, idx) {
  document[elt].src="img/"+ icon + "_" + idx + ".gif"; }

function setNav(btn, idx) {
  document[btn].src="img/"+ btn + "_" + idx + ".gif"; }

function newWindow(url) { 
	var win = open(url, 'screenshot',
				   'width=400,height=300,scrollbars,resizable'); }