Is it possible to create a Silverlight application which can be used to provide a nice user interface for managing SQL Server permissions?
We want to create a simple admin app to allow certain users to create new users, disable old users, and manage specific permissions for those users, but we feel that SQL Server Management Studio is perhaps too complex.
In simple terms yes - every function you perform in management studio is executing SQL at the back end, and virtually all, if not all actions allow you to script out that SQL if you are unsure as to what the SQL syntax for a given action is.
SL will not make a direct connection to the SQL server, you will need to have the SL call a WCF web service which exposes methods / properties for the functionality you wish to implement.
I agree with Andrew but would add that your WCF service could make use of SMO to manage Logins, roles and permissions. See http://msdn.microsoft.com/en-us/library/ms162175.aspx