As Eliran Efron said, change JS line 3 to:
$("#drop").slideDown();
Change HTML line 25-26 to:
<div class="dropdown">
<ul id="drop" class="dropdown-menu" role="menu" aria-labelledby="dLabel">
You were referencing the wrong element with your JS, thats all.
Here is your example modified and working: http://jsfiddle.net/fNrZ3/4/