When VTS is installed, the VTS OPC Server DCOM component is automatically registered with the operating system. This is required for a client to be able to connect to the VTS OPC Server (for any VTS application).
If you wish to unregister VTS as an OPC server, you should run the following command at a command prompt (in Windows Vista, this must be run from an administrator-privileged command prompt): vts /UnRegOPCServer
If you wish to re-enable the VTS OPC Server, you should run the following command: vts/RegOPCServer
This is a VTS-wide setting. It does not need to be done for each application.