Having effects on append won’t work because the content the browser displays is updated as soon as the div is appended. So, to combine Mark B’s and Steerpike’s answers:
Style the div you’re appending as hidden before you actually append it. You can do it with inline or external CSS script, or just create the div as
<div id="new_div" style="display: none;"> ... </div>
Then you can chain effects to your append (demo):
$('#new_div').appendTo('#original_div').show('slow');
Or (demo):
var $new = $('#new_div');
$('#original_div').append($new);
$new.show('slow');