How do I code the theming of a form?

I am trying to upgrade a module from 5.x to 6.x.

Need some help. I can't seem to figure out how to theme a form.

When I click on the menu item item for the form, I get this warning:

warning: Invalid argument supplied for foreach() in includes/menu.inc on line 258.

I see the realms listed, but the form isn't rendered at all. I put a "drupal_set_message" in the "theme_node_multinode" function, and I don't see it when I click on the form. This means that function is failing as soon as it is hit, or not being hit at all.

Here's the code snippet for the form. With the exception of the hook_menu code, it's more or less the same as in 5.x version of patch:

//////////////////
/// hook_menu ////
//////////////////
  // multinode_access
  $items['admin/content/multinode'] = array(
    'title' => t('Multinode user interface'),
    'description' => t('Interface for configuring multiple node access.'),
    'page callback' => 'drupal_get_form',
    'page arguments' => array('node_multinode'),
    'access arguments' => user_access('administer nodes'),
    'type' => MENU_NORMAL_ITEM,
   );  

//////////////////////////////////////
////// Multinode Access Form ////////
/////////////////////////////////////

/**
 * Generate multinode access UI form.
 */
function node_multinode($theme = NULL) {
  global $theme_key, $custom_theme, $user;
  if (isset($uid)) {
    $account = user_load(array('uid' => $uid));
  } else {
    $account = $user;
    $uid = $user->uid; 
  }
  
  // Get whatever is stored in multinode table.
  $existing = array();
  $result = db_query("SELECT * FROM {multinode_access}");
  while ($row = db_fetch_object($result)) {
    $existing[$row->realm] = $row;
  }

  // Get all rule realms from node_access table.
  $result = db_query("SELECT DISTINCT realm FROM {node_access}");
   while ($row = db_fetch_object($result)) {
    $rules[] = $row->realm;
   }    

  // Get all rule realms from modules.  User doing this should have grants in all modules affected.
  $op = 'view';
  $mrules = node_access_grants($op, $account);
  foreach ($mrules as $realm => $grants) {
    $rules[] = $realm;
  }
  
  // Get only unique values
  $rules = array_unique($rules);
    
  // Sort the rule realms
  asort($rules);

  $form['#tree'] = TRUE;
  foreach ($rules as $realm) {
    $form[$realm]['checkbox'] = array('#type' => 'checkbox', '#default_value' => (isset($existing[$realm]->realm) ? 1 : 0)); 
    $form[$realm]['realm'] = array('#type' => 'textfield', '#size' => 25, '#disabled' => TRUE, '#value' => check_plain($realm), '#default_value' => $realm); 
    $form[$realm]['group'] = array('#type' => 'textfield', '#size' => 5, '#default_value' => (isset($existing[$realm]->groupname) ? $existing[$realm]->groupname : '') ); 
    $form[$realm]['logic'] = array('#type' => 'select', '#default_value' => (isset($existing[$realm]->logic) ? $existing[$realm]->logic : 'AND'), '#options' => array('AND' => 'AND', 'OR' => 'OR') ); 
    $form[$realm]['weight'] = array('#type' => 'select', '#default_value' => (isset($existing[$realm]->weight) ? $existing[$realm]->weight : '0'), '#options' => array('0' => '0', '1' => '1', '2' => '2', '3' => '3', '4' => '4', '5' => '5', '6' => '6', '7' => '7', '8' => '8', '9' => '9') ); 
    $form[$realm]['check'] = array('#type' => 'select', '#default_value' => (isset($existing[$realm]->checkstatus) ? $existing[$realm]->checkstatus : '0'), '#options' => array('0' => '0', '1' => '1') ); 
  }

  $form['submit'] = array('#type' => 'submit', '#value' => t('Save changes'));

  return $form;

}

/**
 * Theme function to render the table for the node_multinode 
 * Multinode access UI
 */
function theme_node_multinode($form) {
  $output .= "\n<div id=\"node-multinode-form\">\n";
  $output .= '<div id="desc">'. t('Here you can configure multinode access.  You can only modify values here if TAC/OG Integration is ON. If you turn TAC/OG Integration ON, then later wish to turn it off, you must first UNCHECK all items here and <strong>Save changes</strong> (otherwise, multinode access will continue).') ."</div>\n";
  $header = array(t(''), t('Realm'), t('Group'), t('Logic'), t('Weight'), t('Check'));
  $rows = array();

  foreach (element_children($form) as $i) {
    $block = &$form[$i];
    $rows[] = array(drupal_render($block['checkbox']), drupal_render($block['realm']),
        drupal_render($block['group']), drupal_render($block['logic']),
        drupal_render($block['weight']), drupal_render($block['check']),
      );
  }

  $output .= theme('table', $header, $rows, array('id' => 'node-multinode-table'));

  $output .= drupal_render($form['submit']);

  $output .= "</div>\n";
  $output .= drupal_render($form);
  return $output;
}

/**
 * Process multinode form submission.
 */
function node_multinode_submit($form, $form_state) {
  // Erase all existing settings
  db_query ("DELETE FROM {multinode_access}");

  // Insert new settings
  foreach ($form_state['values'] as $block) {
    if ($block['checkbox'] == 1) {
      db_query("INSERT INTO {multinode_access} (realm, groupname, logic, weight, checkstatus) VALUES ('%s','%s','%s','%s',%d)", $block['realm'], $block['group'], $block['logic'], $block['weight'], $block['check']);
	}
  }
  drupal_set_message(t('The multinode access settings have been updated.'));
  cache_clear_all();
}

This is a general depiction of the form I'm trying to generate, modified for 6.x and specific to node module now:

http://drupal.org/files/issues/OGRConfigureMultinodeUI_ACL.jpg

What I'm getting is this:

http://drupal.org/files/issues/multinode_ui_error.jpg

Can someone who is way more familiar with 6.x than I am tell me what I'm doing wrong here? Thanks.