I need to create a login page that allows users to create a new account or choose from an existing account, the trick here is I want to allow the existing customer to have the ability to choose from a compiled list of members using last name and address.

This is something that my client wants done, currently they have an existing OScommerce site and only want to provide a service that acts like an online customer service rep. I know it sounds confusing, but my client feels that giving the customer this option will "refresh" the customers memory as to member registration... I am contemplating using the mini-store, but I would still need to make modifications to the login page...and suggestions?
Thankx in advance
Jeni