Attached .mdf file security settings

I'm having some problems with SQL Server 2005. I installed the Personal Starter kit but don't have the Express edition installed so I attached the .mdf file to SQL Server 2005. That's ok and I also changed the connection string to integrated security.
<add name="Personal" connectionString="Data Source=MyTestServer;Initial Catalog=Personal;Integrated Security=True" providerName="System.Data.SqlClient"/>
I tried setting the security settings in the Management studio under Security | Logins | BUILTIN\Administrators where I select the User mapping and check the checkbox before the Personal.mdf file. But this doesn't seem to do the trick. How can I set the correct security settings?
Please, does someone here know an answer for this?
|||It seemed that the attached .mdf file got the position on the hard drive (c:\...\personal.mdf) instead of the proper name. After changing that with the sp_renamedb command I could get it to work.