Vista - Retrieving IUSR_ account name - works in 2k3 - truncates in 2k8

Hello,

The following 2 line vbscript retrieves the AnonymousUserName from the
metabase. This works fine for Server 2003, but isn't returning the full
account name in 2008 (seems to not like the "_" character).

Set IIsObject = GetObject ("IIS://localhost/w3svc")
WScript.Echo "AnonymousUserName = " & IIsObject.Get("AnonymousUserName")


Server 2003 Results:

C:\Documents and Settings\Administrator\Desktop>cscript a.vbs
Microsoft (R) Windows Script Host Version 5.6
Copyright (C) Microsoft Corporation 1996-2001. All rights reserved.

AnonymousUserName = IUSR_SI-VS



Server 2008 results:

C:\Users\Administrator\Desktop\>cscript a.vbs
Microsoft (R) Windows Script Host Version 5.7
Copyright (C) Microsoft Corporation. All rights reserved.

AnonymousUserName = IUSR


Can anyone point me in the right direction as to how to get this to work on
both 2k3 & 2k8? Or at least what has changed in 2k8? I see the Windows
Script Host version in 2k3 is 5.6 while 2k8 is 5.7.

Thanks,
-B