How to use drupal_get_form for retrieving a custom content type?

Hi,

How can I use drupal_get_form for retrieving a custom content type? Somehow I don't succeed in that.
What I'd like to do is this:

I created two content types: "document" and "item". The idea is to add general fields to the document type and specific fields to one or more items. By merging document and items together in a view a complete document is created.
The merging is done in a node-document.tpl.php file by using this code:

    // load the context-node's 'metadata'
  global $current_view;
    // * define the context-node's NID as the argument
  $current_view->args[0]=$node->nid;
    // * select the name of the view to embed as $view1
  $view1 = views_get_view('Items');                     
    // * define this section for CSS
    print '<div class="Items">';
    // * display a subtitle for the view section
    //print '<h2>' . t($node->title . ' Items') . '</h2>';
    // send $args to the View's Argument Handler and display $view1 in the context-node
    print (views_build_view('embed', $view1, $current_view->args, false, false)); 
    print '</div>';
  

Now I'd like to add new Items directly in the view by trying to pull in a new item form, so I added this line to the tpl.php file:

print drupal_get_form('item_node_form');

This doesn't work:

warning: Missing argument 1 for node_form() in C:\xampp\htdocs\drupal\modules\node\node.module on line 2025.

This however:

print drupal_get_form('user_login_block');

DOES work.

I tried several different form_id's but somehow I keep on getting the error message. Am I using a wrong form_id? Or isn't this possible at all? Hope someone can give me a little help.

Rick