NT can have arbitrary number of desktops, only one of them normally visible on a given console. All services run on an invisible desktop (I am not aware of any way to make that one visible). Terminal server gives you the ability to make invisible desktops visible. Another way to get an alternative desktop, I believe (I may be wrong here) is to hit ctrl-alt-del. The visual you see is actually a different desktop.

Also, you don't have to have a desktop to run a process, hence telnet server.