A little help with my first app...

[eluser]n0xie[/eluser]
You should use the active record class.

To answer your question

Code:

//controller
function delete($id = NULL)
    {
        $this->load->model('Guestbook_model');
          $this->Guestbook_model->deleteEntry((int) $id);
        $this->load->view('delete_success');
    }

// model
function deleteEntry($id)
{
  // just to make sure we don't do anything stupid
  if ($id > 0)
  {
        $this->db->where('id',$id);
        $this->db->delete('data');
  }
}

A word of caution though. You should always do any destructive action via a POST, not via a GET request, so I would advice against doing it this way. This is to prevent numerous security issues, the most simple being, what if the Googlespider would index your site and go to the url 'example.com/guestbook/index.php/delete/2'?