var navitems = Array('nav1', 'nav2', 'nav3');
var timer;

function nav(whatITEM) {
	clearInterval(timer);
	
	for (i=0; i<navitems.length; i++) {
		if (whatITEM == navitems[i]) {
			document.getElementById(navitems[i]).style.display = 'block';
		}  else {
			document.getElementById(navitems[i]).style.display = 'none';
		}
	}
	
	if (whatITEM) {
		timer = setInterval(nav, 5000);
	}
}