gistfile1.php

<?php
$installer = $this;
$installer->startSetup();

$entityTypeId     = $installer->getEntityTypeId('catalog_category');
$attributeSetId   = $installer->getDefaultAttributeSetId($entityTypeId);
$attributeGroupId = $installer->getDefaultAttributeGroupId($entityTypeId, $attributeSetId);

$installer->addAttribute('catalog_category', 'new_cat_attrb',  array(
'type'     => 'int',
'label'    => 'New Category Attribute',
'input'    => 'text',
'global'   => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
'visible'           => true,
'required'          => false,
'user_defined'      => false,
'default'           => 0
));

$installer->addAttribute('catalog_category', 'new_cat_attrb',  array(
    'type'     => 'int',
    'label'    => 'New Category Attribute',
    'input'    => 'text',
    'global'   => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
    'visible'           => true,
    'required'          => false,
    'user_defined'      => false,
    'default'           => 0
));

$installer->addAttributeToGroup($entityTypeId,$attributeSetId,$attributeGroupId,'new_cat_attrb','11');

$installer->endSetup();