User2sid and Sid2user
"Two small utilities for Windows NT, created by Evgenii Rudny, that allow the administrator to query the SAM to find out a SID value for a given account name and vice versa. User2sid.exe can retrieve a SID from the SAM (Security Accounts Manager) from the local or a remote machine and Sid2user.exe can then be used to retrieve the names of all the user accounts and more". More...