When all else fails, and many other times as well... Script Injector
Friend of Sprocket Rick Lochner of RPC Leadership Associates has a DNN website that we built for him. He is a Leadership Trainer and likes interactive graphics. We made him a new diagram recently that looks like this, and on the live site if you hover over the blocks in the diagram you get a pop-up explaining the block. Try it.
Here's how I made it. I drew it in Photoshop, including the area for the description paragraph, then sliced it up so that the interactive areas were their own individual image files. Then I did a little programming using basic HTML, some DIVs and a little CSS. So onMouseOver, the associated DIV's style changed to visible, and onMouseOut, it changed to hidden. (In a nutshell, of course.)
I'm not saying this is the most elegant way to do such things, and if a DNN guru is reading this and snickering, please comment on how you'd do it differently, but it worked for me and the client.