Pass arguments to a node
The easiest way is to use $argument = arg(2) but more formal and much better way will be to create new menu item based on node/%node:

function yourModule_menu() {
  $items['node/%node/%'] = array(
    'page arguments' = array(1, 2), // Here you can specify which parts of url are page callback arguments (starting with 0)
    'page callback' = 'yourModule_node_with_option',
    'access arguments' =&gt; array('content access'), // Try to avoid access callback = TRUE
    'type' =&gt; MENU_CALLBACK,
  );
  return $items;
}

function yourModule_node_with_option($node, $option) {
  // build your new page here.

  // $option is your extra parameter.
  $output = $node-&gt;nid . ' ' . check_plain($option);

  // This will show you node id and value of parameter
  return $output;
}