Hey thanks!
That works perfect, well almost it does, the only problem i have now is that the pop-up has some white space above the enlarged image. Strange, although the pop-ups on the the example page:
http://forum.fok.nl/showtopic.php/447356
Doesn't have that ugly whitespace. Any clues?
Hmm, i just checked and i think they used an image.php document, with unknown contents...
Also on your example zip file, the image in the pop-up is cropped somehow, it doesn't show the complete image... Argh