how to read csv file in drupal 6
try function form submit like:

function my_module_form_submit($form, &amp;$form_state) {
  $line_max = variable_get('user_import_line_max', 1000);
  ini_set('auto_detect_line_endings', true);
  $filepath = $form_state['values']['file_upload']-&gt;filepath;
  $handle = @fopen($filepath, "r");
  // start count of imports for this upload
  $send_counter = 0;
  while ($row = fgetcsv($handle, $line_max, ',')) {
    // $row is an array of elements in each row
    // e.g. if the first column is the email address of the user, try something like
    $mail = $row[0];
  }
}