DHTML drop-down & JavaScript

Is Dynamic HTML (DHTML) basically a subset of javascript? Or is it just in this case?

Short Question:
I would like to have
ToggleLink1, ToggleLink2, ToggleLink3
display a drop-down graphic and some text below those links when they are clicked (but only one open at a time).

Long Question:
I am using RoboHelp HTML and decided to add the DHTML "Create Drop-down Hotspot and Text..." effect to what I figured was a simple HTML file. But when I view "TrueCode" (which is basically the same as "viewing the html source", I see JavaScript tags. So if I'm using javascript anyway (by adding this DHTML feature), then I suppose JavaScript can help me customize this feature (and not even use the bloatware DHTML in RoboHelp HTML).

Let's say I have links A, B, C, D, and E all on the same row. Each DHTML drop-down hotspot shows a picture A.gif, B.gif, etc., respectively. They toggle (drop-down -- open?, or hide -- close?) when their link is clicked. But can I customize it so that only one is open at a time? If there was an open or close javascript function (maybe with a variable to keep track of an open drop-down, then I think I would have what I want.

Actually, what I am trying to mimic is a tab-pane window. In a typical windows app, if I have tabs A,B,C... and each is clicked, their graphic is displayed (and only for that tab). Except that my links are actually above the "tab-pane window", I would achieve a similar effect if I can close any drop-down that is already open, before opening the one that was just clicked (in my particular group A,B,C...). The RoboHelp HTML source references a .js file with even more bloatware source. I'm warned not to edit it. Even so, I'm not seeing an open/close function (but it may be there). I would think that the code would be much shorter if I could do this in javascript. Any ideas?