I want to modify the registration page to add custom fields which would potentially include
Address Details
Take a look at the customer_setup scripts for reference. For example:
Mage/Customer/sql/customer_setup/mysql4-upgrade-1.4.0.0.0-1.4.0.0.1.php
This file has an example of how to assign attributes to the customer address form (bottom of file):
Mage/Customer/sql/customer_setup/mysql4-data-upgrade-1.4.0.0.13-1.4.0.0.14.php
Best practices would be to create a new module with an install script, and put your code in there to add the custom attributes.
The customer model is an EAV model. EAV is a complicated subject in Magento. A good exercise would be to read up on creating a EAV module -- to understand the basics -- and then come back to adding custom attributes.
Enterprise allows you to add customer attributes via the admin panel, but unfortunately it's more of a pain for CE.
That should get you started. Hope this helps.