If you are using NetBIOS over TCP, you can find the computer a user is logged onto with the command:
nbtstat –a username
That method is not effective for finding multiple sessions, nor does it work when you finally stop using NetBIOS. xFinger.vbs, by Gurgen Alaverdian was written with the interesting idea that you can find a user based on their session to the home directory server. My version of xfinger.vbs adds a prompt for the user name, resolution of IP to Name, and a WMI double check to see if user is logged onto the PC. Unlike nbtstat, you need to have admin rights on the home directory server for this to work.
Update: 4/13/12 adds the ability to copy the data to the clipboard using MS Word. Make sure you have opened Word at least one time with the permissions you are using before trying to run the script.