function FadeGallery(){
	
	$('#header_gallery').fadeOut(600,function(){
		$('#header_gallery').css('background-image','url('+GalleryImages[NextImage]+')');
		$('#header_gallery').fadeIn(600);
		if(NextImage == GalleryImages.length-1){
			NextImage = 0;
		} else {
			NextImage++;
		}
	});
}
window.setInterval('FadeGallery()', 18000);


<!--
var NextImage = 1;
var GalleryImages = new Array(5);
GalleryImages[0] = '../images/gallery/1.jpg';
GalleryImages[1] = '../images/gallery/2.jpg';
GalleryImages[2] = '../images/gallery/3.jpg';
GalleryImages[3] = '../images/gallery/4.jpg';
GalleryImages[4] = '../images/gallery/5.jpg';
GalleryImages[5] = '../images/gallery/6.jpg';
GalleryImages[6] = '../images/gallery/7.jpg';
//-->