PsLoggedOn

You can determine who is using resources on your local computer with the "net" command ("net session"), however, there is no built-in way to determine who is using the resources of a remote computer. In addition, NT comes with no tools to see who is logged onto a computer, either locally or remotely.
The PsLoggedOn application was developed to be an applet that displays both the locally logged on users and users logged on via resources for either the local computer, or a remote one. If you specify a user name instead of a computer, PsLoggedOn searches the computers in the network neighborhood and tells you if the user is currently logged on.
PsLoggedOns definition of a locally logged on user is one that has their profile loaded into the Registry, so PsLoggedOn determines who is logged on by scanning the keys under the HKEY_USERS key. For each key that has a name that is a user SID (security Identifier), PsLoggedOn looks up the corresponding user name and displays it. To determine who is logged onto a computer via resource shares, PsLoggedOn uses the NetSessionEnum API. Note that PsLoggedOn will show you as logged on via resource share to remote computers that you query because a logon is required for PsLoggedOn to access the Registry of a remote system.
Usage:
psloggedon [- ] [-l] [-x] [\\computername | username]
- Displays the supported options and the units of measurement used for output values.
-l Shows only local logons instead of both local and network resource logons.
-x Dont show logon times.
\\computername Specifies the name of the computer for which to list logon information.
username If you specify a user name PsLoggedOn searches the network for computers to which that user is logged on. This is useful if you want to ensure that a particular user is not logged on when you are about to change their user profile configuration.