>Well, I am somewhat new to the "service" stuff. So, is it correct to say that a service is, by definition, always active? And that it is not tied to a particular user account?

About active part. A service could be configured to be Disabled, Manual or Automatic. It also can be started (if it's not Disabled) and stopped using NET START/STOP command, Windows API or Shell.Application object. See Windows Service Status for some more info.