Register: Don't request address | Checkout: Require address

As far as I am aware, the normal register file and the checkout register file are two separate files.

Is there an extension out there already or can someone advise me how I can allow users to register with just their first name, last name and email address but then during checkout, if they do not have an address, require them to submit an address for products to be delivered?

Many thanks
Keiron

have a look at this
http://www.opencart.com/index.php?route ... on_id=4811