Our intranet uses NT authentication. I need to know the user ID of the person accessing a page. For example (this is not actually what I need to do but the idea is similar), suppose you wanted to print on the page: Welcome, [username]. Is there a property somewhere that you can read to get the name? (The user must have been authenticated to run the page script, so the user name must be stored somewhere...)

It's OK to make this browser-dependent, since everyone in the organization uses IE4.