Jairo,
The easiest way to integrate it with an Active Directory server is to set up LDAP Authentication for the users. The NetSight server does not need to be installed on a machine that is part of the domain.
I believe there is a help topic on configuring that as well, but you would set it in the Authorization/Device Access window. I'd recommend when setting it up that you turn on "Authenticate to OS on LDAP Failure" as well in case you cannot access the LDAP server. That will allow you to use your local user.
Tyler