How to: Hide an Instance of SQL Server Database Engine
SQL Server uses the SQL Server Browser service to enumerate instances of the Database Engine installed on the computer. This enables client applications to browse for a server, and helps clients distinguish between multiple instances of the Database Engine on the same computer. You may wish to run the SQL Server Browser service to expose some instances of the Database Engine, but still hide other instances. Use SQL Server Configuration Manager to hide an instance of the Database Engine.
In SQL Server Configuration Manager, expand SQL Server 2005 Network Configuration, right-click Protocols for <server instance>, and then select Properties.
On the Flags tab, in the HideInstance box, select Yes, and then click OK to close the dialog box. The change takes effect immediately for new connections.