Alternative themed forms for a single custom content type
My first thought (in Drupal 6) would be to use hook_form_alter to set a different #theme value in the form depending on the path.

eg

mymodule_form_alter(&amp;$form, &amp;$form_state, $form_id) {
 if ($form_id = 'my_form_id') {
  if ($_GET['q'] == 'somepath') {
   $form['#theme'] = 'function_one';
  } elseif ($_GET['q'] == 'someotherpath') {
    $form['#theme'] = 'function_two';
  }    
 }
}