IIS ASP.Net - What identity is your page running in?
There are at least three identities that I know of when you run an ASP.Net page on an IIS server. They are:

- At the page level: Page.User.Identity
 - At the thread level: System.Threading.Thread.CurrentPrincipal.Identity
 - At the process level: System.Security.Principal.WindowsIdentity.GetCurrent()
 
Then there are authentication and impersonation modes to set. In Vista, the Computer Management configuration is not as neat as XP or Server 2003, as follows:

The different identities have values as follows (the IIS server is mozart and the web browser user is UserA):
| Authentication Mode | ASP.Net Impersonation | Process | Thread | Page | 
|---|---|---|---|---|
| Anonymous | False | NT AUTHORITY\ NETWORK SERVICE  | - | - | 
| Anonymous | True | NT AUTHORITY\IUSR | - | - | 
| Windows | False | NT AUTHORITY\ NETWORK SERVICE  | mozart\UserA | mozart\UserA | 
| Windows | True | mozart\UserA | mozart\UserA | mozart\UserA | 
References: 
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