You can view information about users which are connected to a terminal server on the Users tab in Terminal Services Manager.
You can interact with any of the connected users you see simply by right clicking him.
You will call up a shortcut menu that contains several options which allow you to disconnect users, send a message to them, or even remotely control their sessions. The shortcut menu even allows you to view the user activity, failed logons of the user, to reset user session or to log off user.
There are graphs for each user on the bottom part of the window. Graphs by CPU Usage, Memory Usage, Processes, RDP Incoming and Outgoing Bytes are available.
Choose a tab above graphs to view a parameter.