Darn, I made a long reply last night before going to bed but it seems to not have posted here.
The scrolling and pop-up window of the gallery you showed me is using JavaScript. You could also use Flash to create these effects. The gallery example you gave works in IE 7 but breaks on Firefox 3 (the two I tested it on). It could be made to work cross-browser though.
The scrolling is produced with a
window.scrollTo() or
window.scrollBy() type functions, where you target the <div> window and you can specify it's horizontal or vertical scroll with a mouse click event.
The pop-up window is produced with JavaScript and CSS using the
display: none; and then showing the pop-up div again when someone clicks a thumbnail image.
document.getElementById('pop-up').style.display = 'block';
Of course there are other styles and scripting involved to make it look and work smoothly, but these are the basic principles involved with this gallery.
There is a gallery I created that does not have the vertical scrolling effect you want, but does have some interesting image display functionality using JavaScript, like an image-loading animation and stuff like that. You can view it here, just click on one of the thumbnails to see the image display page.
http://www.freshgrok.com/samples.php
Let me know if you want to use any of the scripting there.
Enjoy