I don't know if this is something that's peculiar to 1.9.0.0 but I couldn't get either Mage::getConfig()->getNode()->stores->{$code}
or Mage::getModel('core/store')->loadConfig($code)
(which in fact calls Mage::getConfig()->getNode()->stores->{$code}
) to return anything.
The first was close... with a subtle change in form, this gets a result, though it's waaay more info than you need:
$store = Mage::getConfig()->getNode('stores')->{$code}
What worked for me, to get just the store id, was this:
$storeId = Mage::getConfig()->getNode('stores')->{$code}->system->store->id;
...still inefficient, of course, loading all that config info just for one little number. But hey, that's Magento for you.
Mage::app()->getStore($storeCode)->getId();