Linda's Web Technologies

I've followed all the instructions from http://guides.rubyonrails.org/getting_started.html and I've a blog set up, that has a form, allows a user to create a post, comment, edit, add tags, has some security to protect who can post,and edit, delete etc.  Only problem is that when I click delete post, I get the expected message "are you sure?" with the option to continue or to cancel.  However when I click cancel it goes ahead and deletes the comment anyway.  So I'm trying to find out how I can fix this. 



In the views post index there is the line
<td><%= link_to 'Destroy', post, :confirm => 'Are you sure?', :method => :delete %>
In the controllers (which I suspect is where I have to change something) I have this code
def destroy
    @post = Post.find(params[:id])
    @post.destroy
    respond_to do |format|
      format.html { redirect_to(posts_url) }
      format.xml  { head :ok }
    end

I've had a look around to find the code for the form_for method and I can't find it.  Perhaps that's where I should be looking?