[ask] how upload and validate the form

[eluser]siubie[/eluser]
i have change my code to this one :

Code:

function addSponsor(){
        $data['judul']=$this->Title;
        $data['heading']="Penambahan Sponsor";
        $data['heading2']="Penambahan Sponsor Pimnas 2009";
        $data['nama']=array(
            'name'=>'nama'
       );
        $data['gambar']=array(
            'name'=>'gambar',
            'type'=>'file'
        );
        $data['url']=array(
            'name'=>'url'
        );
        $this->form_validation->set_rules('nama', 'Nama Sponosr', 'trim|required|xss_clean');
        $this->form_validation->set_rules('gambar', 'Gambar Harus Di Isi', 'callback__gambar');
        $this->form_validation->set_rules('url', 'Link Ke Sponsor', 'trim|required');
        if ($this->form_validation->run() == FALSE)
        {
            $this->load->view('controlPanelAdmin/addSponsor.php',$data);
        }
         else{
                            $masukkan=$this->pimnas_model->masukkanSponsor();
                                if($masukkan){
                                  $data['sukses']="Katalog Berhasil Dimasukkan";
                              }
                              else{
                                $data['sukses']="Katalog Gagal Dimasukkan";
                              }
                            $this->load->view('controlPanelAdmin/succedSponsor',$data);

                        }

        }

        function _userfile(){
        $config['upload_path'] = './asset/img/sponsor/';
        $config['allowed_types'] = 'gif|jpg|png';
        $config['max_size']    = '100';
        $config['max_width']  = '1024';
        $config['max_height']  = '768';
        $this->upload->initialize($config);
        if (!$this->upload->do_upload('gambar'))
        {
            $this->form_validation->set_message('_gambar',$this->upload->display_errors());

            return false;
        } else {
            return true;
        }
    }

no error but the file not uploaded to ./asset/img/sponsor i am using windows and xampp 1.6.4
and when i add validation rule

Code:

$this->form_validation->set_rules('gambar', 'Gambar Harus Di Isi', 'trim|required|callback__gambar');

the result is this form not valid