Kirupa Photo Gallery Tuto... add buttons

http://www.kirupa.com/developer/mx2004/thumbnails.htm

I have been using this tutorial to build a photo gallery, which is excellent.

I’d like to add buttons to the scrolling feature so that when the user clicks an arrow, the thumbs scroll 3 or 4 at a time and stop. Is that an easy modification or am I way past my level of capability on this one (still fairly new to everything)? Can someone point me in the right direction?

Thanks!