How to configure member ship with a database other than aspnetdb

You need to create a membership provider to connect to your custom tables for authentication. MSDN has some documentation on the subject. You can also view a video on the subject at ASP.NET. Here are the links.

• http://msdn.microsoft.com/en-us/library/f1kyba5e(v=vs.100).aspx
• http://www.asp.net/web-forms/videos/how-do-i/how-do-i-create-a-custom-membership-provider

The main method for validation is going to be the ValidateUser method, you will override this method to provide authentication.

public sealed class CustomMembershipProvider : MembershipProvider
{
    // implement other methods

    public override bool ValidateUser(string username, string password)
    {
        try
        {
            var user = // GET USER OBJECT HERE
            if (user != null)
            {
                string name =  // set username

                // Set your forms authentication ticket
                FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(1, user.ID.ToString(), DateTime.Now, DateTime.Now.AddMinutes(30), false, name, FormsAuthentication.FormsCookiePath);

                HttpCookie authCookie = new HttpCookie(FormsAuthentication.FormsCookieName, FormsAuthentication.Encrypt(ticket));
                HttpContext.Current.Response.Cookies.Add(authCookie); 
                return true;                    
            }
        }
        catch
        {
        }

        return false;
    }

    // Other implementations
}

If you have roles in your application you may also want to implement a custom role provider:

http://msdn.microsoft.com/en-us/library/8fw7xh74(v=vs.100).aspx