Security :: Membership Provider With Same Usernames Allowed?

I'm trying to build a website which has a two-tier membership system, a bit like Basecamp. The first level of membership will be the administrators, who must have unique usernames. The second level will be the clients of the administrators, so they must allow duplicate usernames (e.g 'johnsmith' can register under 'administrator1' but 'johnsmith' can also register under 'administrator2'.To give a bit of background on this, evenutally each administrator will have their own sub-domain (exactly like Basecamp) using their username as a sub-domain, like this:http://administrator1.example.comhttp://administrator2.example.comThen each administrator may have lots of clients, with their own username as part of the URL when they log in. e.g:[URL]this type of membership system? Presumably it has to be a custom provider? Would I be better just creating my own database table structure (perhaps 2 tables, one for each membership type) then build the code around these, with my own authentication etc?What I'm thinking is a database schema something like this:AdminMembers table:Id (primary key)Username (must be unique)EmailPasswordClientMembers table:Id (primary key)UsernameEmailPasswordAdminMembersIdWould something like this work? If so, would I need to make this into a custom provider? Any good references for this type thing?I'm a total ASP.NET MVC newby (and have limited ASP.NET experience anyway) but I'm trying to use this project to learn,