Create duplicate registration form with extra fields
Use the LoginToboggan module 


  The LoginToboggan module offers several modifications of the Drupal login system in an external module by offering the following features and usability improvements:



Allow users to login using either their username OR their e-mail
address.
Allow users to login immediately.
Provide a login form on Access Denied pages for non-logged-in
(anonymous) users.
The module provides two login block options: One uses JavaScript to
display the form within the block immediately upon clicking "log
in". The other brings the user to a separate page, but returns the
user to their original page upon login.
Customize the registration form with two e-mail fields to ensure
accuracy.
Optionally redirect the user to a specific page when using the
'immediate login' feature.
Optionally redirect the user to a specific page upon validation of
their e-mail address.
Optionally display a user message indicating a successful login.
Optionally combine both the login and registration form on one page.
Optionally have unvalidated users purged from the system at a
 pre-defined interval (please read the CAVEATS section of
 INSTALL.txt for important information on configuring this
 feature!).
Integrates with Rules module to do various tasks when a user
 validates via email validation process (see
 http://drupal.org/node/880904 for an example)


Demo is here http://doaproject.org/user/register