Display magento products by category ID

Question

I need to know how can I display products in a page like (cart, below total) only few products by ID. Eg: products with id 2,3,4 and 5.

Answer 1

$categoryid = 123;
$_category = Mage::getModel('catalog/category')->load($categoryid);
$productCollection = Mage::getResourceModel('catalog/product_collection')
->addCategoryFilter($_category);