How to use nodereference_select in custom form (set default value) D6
I've managed to use such a field widget in a custom form in the following manner

  $field = content_fields('&lt;field name on a node type&gt;', '&lt;node type that uses this field&gt;');
  $form['#field_info']['&lt;field name on a node type&gt;'] = $field;
  $form += content_field_form($form, $form_state, $field);


I don't know if it would work without a node type actually having such a field.
I had a node type with that reference so I could "invoke" that.

The resulting form element does not look like a simple select element, it does not have '#options' and '#default_value' is fancy too.