Reusing a node form in a separate page
function mymodule_node_add() {
 module_load_include('inc', 'node', 'node.pages');

  //I'm doing a print here instead of returning because I'm calling this page
  //in an AJAX popup, so I don't want the whole page to output, only the form.
  $form = node_add($node_type);//You need to pass content type here. THat's it.
  print render(drupal_get_form('mymodule_node_add_form'));
}