ASP.NET Membership With AJAX and SQL Server Help Required

This is a small and personal project, I am developing a website so that I can learn as I go and using sql server express 2005 and VS 2010. It currently consists of just a few pages and is almost entirely written in jquery and javascript but already lots of dynamic content and articles are loaded using ajax through an asp.net script to manipulate an SQL Server database. I have developed an interface where users can choose their favourite articles, rate and sort various content but it is not saved and lost when they close the browser. What I would like is someone that can advise, help and teach me how to implement a basic secure membership login system. I have read a few basic tutorials on MSDN but im not sure they really help me as they are tailored to creating permissions for "members only" folders and html pages. What I need is to integrate members information into the sql database so that each user seemlesly stores and retrieves there own customizations, posts, ratings and so on. I am eager to learn, one thing I am not sure about is if I must use a seperate page ending in ".aspx" to get the login/signup controls? So far I have been using html and javascript and calling asp.net through ajax so I dont have to use ugly extensions and I can display popup forms and post through ajax. As I dont have much experience, not an academic and dont know many people with programming interests it is always nice to find people willing to help so im sure there would be lots of oportunities for future work. Thanks for your time.