How do I create a web site membership page?

Hi,

I have created the below web site using visual studio 2008 (asp.net 3.5, C#) and SQL Server 2005 within a linq datacontext....

http://www.tradeselector.co.uk/Customers.aspx

The site is fine in regards to new users, in that when the "Next" button is clicked (top row on the web site) the user is redirected to a child page displaying the details from their insert through a customer_id (identity column for the data they just inserted) query string variable but I would like to allow returning users the option to login to retrieve their details through my child page. What would be the easiest way to create this type of membership login page? On the login page I would also like forgotten password options and username validation checks etc.

Thanks. 
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