AJAX, Rails, and dynamic loading of forms

<div id="preview">  </div>

<%=    link_to_remote image_tag('whatever.jpg'),
       {:controller => 'something', :action => 'replace_thumbnail', :id => @thumbnail.id},
       :update => 'preview' %>

def replace_thumbnail
  image = Image.find(params[:id])
  render :partial => 'edit', :object => image, :layout => false
end