Quick hack, make sure to run only once, paste at header of theme file. Adds custom field to category. Magento.

CategoryCustomField.php

<?php
require_once('app/Mage.php');
Mage::app()->setCurrentStore(Mage::getModel('core/store')->load(Mage_Core_Model_App::ADMIN_STORE_ID));
$installer = new Mage_Sales_Model_Mysql4_Setup;
$attribute  = array(
    'type' => 'text',
    'label'=> 'Custom Title',
    'input' => 'textarea',
    'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
    'visible' => true,
    'required' => false,
    'user_defined' => true,
	'wysiwyg_enabled' => true,
    'visible_on_front' => true,
    'is_html_allowed_on_front' => true,
    'default' => "",
    'group' => "General Information"
);
$installer->addAttribute('catalog_category', 'custom_title', $attribute);
$installer->endSetup();
?>