You are genies,

Thank you so much.

But is it somehow possible to open the main image as lightbox. (I managed it to open in it lightbox but the lightbox always starst with the first image)

getProduct();
    $_helper = $this->helper('catalog/output');
    $_gallery = $this->getGalleryImages();

    $_resize = 265;
?>

	.product-img-box .more-views li.slide-current a{ border:2px solid #aaa; }
	.product-img-box .product-image-zoom img { cursor: pointer; }
	#slide-loader{ visibility:hidden; position:absolute; top:auto; left:auto; right:2px; bottom:2px; }

function slide(url,num,gallery){
    if (typeof slide.loading == 'undefined') slide.loading = false;
	if(slide.loading) return false;

	var loader = new Image();
	$(loader).observe('load', function(){

		$('slide-loader').setStyle({'visibility':'hidden'});

		$$('div.more-views li').each(function(el,i){
			(i==num) ? el.addClassName('slide-current') : el.removeClassName('slide-current');
		});

		var dummy = new Element('img', { src: url }).setOpacity(0);
		new Insertion.After('image', dummy);
		new Effect.Opacity(dummy, { duration:.5, from:0, to:1.0 });
		new Effect.Opacity($('image'), { duration:.5, from:1.0, to:0,
			 afterFinish: function(){
			 	$('image').writeAttribute('src',url).setOpacity(1).observe('click',function(e){
				 	Event.stop(e);
			 		return false;
				 })
			 	dummy.remove();
			 	slide.loading = false;
			 }
		});
	});

	$('slide-loader').setStyle({'visibility':'visible'});
	loader.src=url;
	slide.loading = true;
return false;
}

	<?php
        $_img = 'helper('catalog/image')->init($_product, 'image').'" alt="'.$this->htmlEscape($this->getImageLabel()).'" title="'.$this->htmlEscape($this->getImageLabel()).'" />';
        echo $_helper->productAttribute($_product, $_img, 'image');
    ?>
    <img id="slide-loader" src="getSkinUrl('images/opc-ajax-loader.gif') ?>" />

    <img id="zoom_out" src="getSkinUrl('images/slider_btn_zoom_out.gif') ?>" alt="__('Zoom Out') ?>" title="__('Zoom Out') ?>" class="btn-zoom-out" />

    <img id="zoom_in" src="getSkinUrl('images/slider_btn_zoom_in.gif') ?>" alt="__('Zoom In') ?>" title="__('Zoom In') ?>" class="btn-zoom-in" />

//

 0): ?>

    __('More Views') ?>

            <a href="helper('catalog/image')->init($this->getProduct(), 'image', $_image->getFile()); ?>" onmouseover="slide('helper('catalog/image')->init($this->getProduct(), 'image', $_image->getFile())->resize($_resize) ?>',,'getGalleryUrl($_image) ?>'); return false;"><img src="helper('catalog/image')->init($this->getProduct(), 'thumbnail', $_image->getFile())->resize(56); ?>" alt="htmlEscape($_image->getLabel()) ?>" title="htmlEscape($_image->getLabel()) ?>" />

Is there a way to replace the pop-up windows with a fancybox or lightbox window on click?

Sorry about being greedy, but a fancybox would just make this perfect.

Thanks.