Admin and normal users, access rights

Hi i have a site which has users, users can log in, when they login i want to ensure they only have access to specific folders and have no rights at all to go into the adminfolder.  I have some questions which are
1)Should admin details and user details be in the same table in my db, and assigned an id to identify their role e.g 1 for admin, 2 for normal user.
2)I was readin up about something regarding   System.Security.Principal is this what i will be using to check a users role?
 
Thanks for your help and advice.
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