Are you just looking for the current user?
If you click on the start button, or press the windows button, it tells you who you are at the top of the right pane.
You can open a command prompt and it should open you up in your folder - C:\users\"username"
I was thinking if you wanted to know who was logged in, you could go to task manager and show processes from all users.
I believe you can also open up the Remote Desktop Services Manager and find out who has active sessions on the local machine, as well as remote machines.
Hope that at least gets you pointed at an answer.