Hi Oggy,
I use the method Bruce suggested for my technical requirements of knowing whos logged in. I store individuals name etc within their respective sessions. I then snoop into the active sessions (quickly).
If you want a helpdesk or realtime solution i'd recommend Zopim, which was bought recently by ZenDesk, but I think you might still be able to use it as a stand alone product (if not their will be other similar ones).
It gives my helpdesk realtime information of who is logged in and what they are doing. My helpdesk can even "break in" and have a conversation with them. They can request help, like you see on websites these days.
Its very cool and improves helpdesk efficiency significantly.
Technically you just inject some JS on each page in your NT app.
Costs $US14-59 a month per helpdesk agent, you might need a ZenDesk account also.
Obviously, i'm not affiliated in any way, I just like their product and I'm lazy.
Regards
Bill