Thanks for the reply.

So changing the code in the locations indicated will result in a checkout flow like this:

Customer hits checkout button
Customer goes to Account Creation/Login
Customer then taken to new shipping address screen with address book
Customer either enters new address or selects one from address book
Customer then taken to Checkout Step 1 and they Checkout normally, still being able to go back to the New Address screen

The files to change are includes/templates/template_default/common/tpl_header.php
and includes/templates/template_default/templates/tpl_checkout_shipping_default, correct?

Thanks,
Doug