Hello keith,
You can give it any farm name you want. Just make sure you have pushed the 7170 remote agent to all the server that are part of the farm (sql server, front end web server, etc) Once this is done typically when you open backup exec you will get an alert that a share point farm has been detected and you should see it in you selection. Also make sure the remote agents have there publishing setup to publish back to the media server
Harry