magento Collections Category Collection of a specific store and specific level
Example
$rootId = Mage::app()->getStore($storeId)->getRootCategoryId();
$categories = Mage::getModel('catalog/category')->getCollection()
->addAttributeToSelect('*')
->addFieldToFilter('path', array('like'=> "1/$rootId/%"))
->addAttributeToFilter('level', 2)
->addAttributeToFilter('is_active', 1);
