If you have a computer that joins to a domain, you can use LDAP to bind to the domain name controller and find a lot of information. Here is how you do it:
1. open a "cmd" window, and do: echo %logonserver% . This tells you the domain controller's name
2. download sysinternals AD explorer software, and connect to the domain controller
3. On the left tree, suppose your company's domain is abc.com, click on "DC=abc,DC=com"
4. In the subtree, click on "OU=...", and keep click on "OU=..." in the subtrees, until your find all the users with "CN=...". There you can see all the users of the domain, and all other information.