I have never used Entity Framework in a project before so I am not sure where to begin. I have I am using the membership tables that are created when using ASP.Net membershi
If you want to have one EF model which links your membership tables and application tables, you can add the ASP.NET Membership tables to your existing database using the aspnet_regsql.exe utility. Some links:
Once you have the Membership tables installed, you can generate EF Code classes that match the membership schema. I posted a detailed walkthrough on how to do that here:
Generating EF Code First model classes from an existing database