If I am remembering correctly, you would edit
/include/ajax.tickets.php
And have it query the AD server for the fields you want. You could utilize something like adLDAP (http://adldap.sourceforge.net(http://adldap.sourceforge.net)) or you could write it entirely yourself with out using a third party class.
As a side note I'm not sure that I would recommend this sort of thing unless you have the site behind some sort of authentication system or is only available internally where you work.