magento set store id programatically

$store_id = 'your_store_id_here';
$mageRunCode = 'store view code';
$mageRunType = 'store';

Mage::app()->setCurrentStore($store_id);
Mage::run($mageRunCode, $mageRunType);

Reference:

http://stackoverflow.com/questions/9870417/magento-set-store-id-programatically