This is the easy way :

$productid=710;   // your product id to update
$storeid=1 // for the store (0 for default)
Mage::getModel('catalog/product_status')->updateProductStatus($productid, $storeid, Mage_Catalog_Model_Product_Status::STATUS_ENABLED);

//or Mage_Catalog_Model_Product_Status::STATUS_DISABLED