function preloadImages() {
	if (document.images) {
		for (var i = 0; i < preloadImages.arguments.length; i++) {
			(new Image()).src = preloadImages.arguments[i];
		}
	}
}

function swapimage(this_image){
	document.images[this_image].src = 'images/nav/' + this_image + '_o.gif';
}
		
function restoreimage(this_image){
	document.images[this_image].src = 'images/nav/' + this_image + '.gif';
}