Hello vPro Experts!
I would like to pass on some information that I discovered a while ago, based on a Microsoft Premiere Support ticket. I was having trouble getting the Microsoft Out-of-Band (OOB) Management Console functioning from a Windows XP system. I tried everything on a fresh, standard build of Windows XP, but nothing would work.
After working with Premiere Support, we finally discovered that Windows XP Service Pack 3 (SP3) was required for proper functioning of the Microsoft OOB console.
This behavior is actually related to some functionality that was added in SP3, specifically in the winhttp.dll library. There is a function called WinHttpSetOption in the WinHttp library, which is called with a parameter enabling the WinHttp Option Flag named WINHTTP_ENABLE_SPN_SERVER_PORT. This flag enables the WinHttp library to include the server port in the Kerberos Service Principle Name (SPN), since the AMT web service is running on a non-standard HTTP port (16993).
The Windows XP Service Pack 2 (SP2) version of the WinHttp library does not include this capability, and consequently fails to authenticate. In order to properly connect to ConfigMgr-provisioned AMT devices with the Microsoft OOB Console, please make sure your helpdesk / support systems are running Windows XP SP3.
If you have any questions, feel free to post them in the comments section, and I will do my best to answer them. 
Trevor Sullivan
Systems Engineer
OfficeMax Corporation