var numberofheaders = 2;
var currentheader = 1;
var timebetweenheaders = 1000 * 10;	// 10 seconds

// preload
for (var i = 1; i <= numberofheaders; i++) {
	var image = new Image();
	image.src = '/fileadmin/images/headers/background_' + i + '.jpg';
}

function changeheader() {
	currentheader++;
	if (currentheader > numberofheaders) {
		currentheader = 1;
	}

	document.getElementById('top').style.backgroundImage = 'url(/fileadmin/images/headers/background_' + currentheader + '.jpg)';

	setTimeout('changeheader()', timebetweenheaders);
}

setTimeout('changeheader()', timebetweenheaders);