There's a few approaches you could take.  The first one would be to
clone one of the previous task chunks and appendChild to the form.  A
nice way to do this is write a behaviour that clones a copy as soon as
the page is loaded (while the form values are still blank) then makes
clones from that as needed.  The second is that you could basically do
what add_task_link does:

Event.addBehavior({
  '#add_task_link:click': function() {
    $('taskform').insert(<%= render(:partial => 'project/task', ...).to_json);
  }

--
Dan Webb
http://www.danwebb.net