Determining registered customers programatically in Magento - magento

Question

Is there any way to determine which customers actually registered for an account and have a password (as opposed to guest checkout customers) in Magento? Specifically I am trying to identify where this information might be stored in the database, or how I might be able to determine this information programatically.
We are in the process of migrating to a new shopping cart and only want to make "accounts" on the new cart for people who actually had accounts on Magento. If we make accounts even for those who did guest checkout, people might have accounts on the new site and not even know it.

Answer 1

You can find all registered customers in the customer_entity table.
If you want to export all customers via the database make sure you export the following tables as well:
customer_address_entity
customer_address_entity_datetime
customer_address_entity_decimal
customer_address_entity_int
customer_address_entity_text
customer_address_entity_varchar
customer_eav_attribute
customer_eav_attribute_website
customer_entity
customer_entity_datetime
customer_entity_decimal
customer_entity_int
customer_entity_text
customer_entity_varchar
customer_form_attribute
If you want to do this by code you can get all registered customers like this:
$collection = mage::getModel('customer/customer')->getCollection();

Answer 2

When a customer places order in Magento using guest checkout, customer information is stored only in quote and order. Customer is not created in the system in that case.
So all customers have created account personally, registered during checkout or were created from admin.
So if you don't have any customizations that are creating customers on guest checkout, you can migrate all customers.
DB:
All records of customer_entity, customer_address_entity and corresponding eav attributes.
PHP:
Using collections
Mage::getModel('customer/customer')->getCollection()->addAttributeToSelect('*');
Mage::getModel('customer/address')->getCollection()->addAttributeToSelect('*');