IIS - ASP : Retrieving domain, IIS Session TimeOut

[eL_NiNo]

I'm now using IIS to authenticate our NT users, but a few questions now rise :

1) I can retrieve the "computername\logon" with the request.servervariables("LOGON_USER") but is there a way to tell its domain ?

2) I want to tell IIS that the user has logged out, hence a new authentication is required (see logout), how can I achieve this ?
This problem occurs when the user logged out of the intranet web site, IIS still consider him as logged on and don't ask a new authentication/session...

Thanks in advance !