I want to do that.
First thanks to everyone who posted an answer to the question.
The answer was remarkably simple, and Navarr Barnier had it -- he said if you use jQuery (which I do) it's as simple as $(selector).slideDown().
To see how it works, check out the Testing menu at the top of the page.
There are two commands in the menu, Hello Walter and Goodbye Walter.
They add and remove a picture of Walter White at the top of the page.
That was exactly the effect I was looking for!
This doesn't work on the Scripting News home page, and I'm sure to take the Testing menu out at some point in the near future. So this will not necessarily make sense if you view the page a few months or years from now. Sorry! Still diggin.