Creating a temporary content type on the fly?
$node_type = array(
  'type' =&gt; 'temporary_node_type', // This is the machine name.
  'name' =&gt; t('Temporary Node'), // This is the human name.
  'base' =&gt; 'node_content', // If you set this to your module name, then
                            // *your module's* hook_insert(), hook_delete(),
                            // etc. will get called in addition to
                            // hook_node_*()
  'description' =&gt; t('Description.')
  // A full list of options is at http://api.drupal.org/hook_node_info.
);

$node_type = node_type_set_defaults($node_type);

node_type_save($node_type);

// Do something with your node type. You can also add fields here if you
// would like.

node_type_delete($node_type);


Note 1: People with the "administrator" role will see this type on node/add every once and a while, depending on how often you do this.

Note 2: You want to use something more then a hard-coded string for your type attribute to avoid collisions.