function init (navId) {
	var nav = document.getElementById(navId);
	var navs = nav.getElementsByTagName('a');
	document.preload = new Array();
	for (var i=0; i<navs.length; i++) {
		document.preload[i] = new Image;
		// images relative to page, not script
		document.preload[i].src = 'layout/' + navs[i].id + '_over';
		//alert('preloaded ' + document.preload[i].src);
	}
	//alert('done preload');
}