I wouldn't call it simple--and while I sometimes have to catch myself using "simply" in a response, I usually hesitate to call anything simple to explain.
I don't know that you will find a tutorial that will mirror what your example page has. What you'll need to know is how to code button behaviors for rollover and clicking of the thumbnail images. And because you can go from any one image to another, you will need to learn how to use actionscript tweening for the fade-in effect and the code needed for swapping the depths of the larger images so that the one fading in always moves to the top. The actual commands you will use depend on which version of actionscript you plan to use.
If you search Google you might find a slideshow tutorial that has some of the features that I outlined... or maybe all of them between a few different ones. Try search terms like "AS# slideshow tutorial" where you substitute 2 or 3 for #.
One recommendation I will make it get a simplified functional version working before you otherwise design yourself into a corner. Just have two buttons (or movieclips as buttons) and two images (movieclips) and get that working first. Don't sweat the aesthetics.
Thanks Ned, I have a bit of experience working with AS, but mainly in making alterations to existing script. Let me see what a search on the terms you recommended turns up.
For the tweening, there is the built-in Tween class (both in AS2 and AS3). And that should work well enough for the purposes indicated. Others will recommend using a third party tweening class like tweener or tween-lite/max, but for getting started I figure the built-in is the better option.
Ned, are you a Flash developer? Perhaps you can answer a few questions.
Like conservation.org, I'm only using four images.
I'm assuming I can place all four images on a single timeline.
Can the small navigation thumbnails be placed on a separate layer, with actionscript that will control
the display of the larger images on mouseover?
And if I'm not asking too much, how does one use a tween to control fade-in and fade-out between different images
on a timeline?