You want to know the NT user-name of the person using the Web browser?
If so, I would very much hope that is impossible. Would you want Web site owners to be able to get hold of your user-name, just by the fact that you browsed their site? I think not!
I think there are ways to integrate authentication on a Web site with authentication on the operating system. I don't know much about these, but I would guess that these still do not allow the server-side code to get hold of the user name or password, just whether they were valid or not.
Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.
Agreed, in general... but the question did specifically mention an intranet website, where that sort of thing is more acceptable. And for Windows environments there's jCIFS which includes NTLM authentication. If you use this to authenticate your users then you automatically know their user ID.