The slideDown method only works when an element has display: none. So the following will do nothing:
But if you hide the element first, it suddenly works:
One of the most frustrating parts of the slideDown docs (and the jQuery docs in general) is that they don't mention this requirement ;_;
As far as where to put it, it can be anywhere after you insert the contentTobeLoaded HTML into the #ajax <div>. Of course, you'll still have to tinker with it, because there's an unsightly jump after the content is inserted and hidden, but before it actually slides...
Ah, you changed it so that the last sentence is actually moot. Good job! All you need to do is add the hide/slideDown calls and you're good.