During an SBS deployment, I ran into a few machines at my customer's site that were running Windows XP Media Center Edition (MCE). As most of you know, the only machines that are technically eligible to join a Windows domain are "Business" class operating systems, such as Windows XP Professional, Windows Vista Business, Windows Vista Enterprise, Windows 7 Professional and Windows 7 Enterprise (although not technically "business" class, Windows Vista/7 Ultimate Editions are also able to join domains, since they're supposed to be everything-but-the-kitchen-sink editions).
And, as luck would have it, the customer has critical LOB applications installed on these machines and some other pieces of legacy software for which the media is no where to be found, so a fresh install with Windows XP Professional media is out of the question.
No problem, right? I've upgraded dozens of Windows XP Home PCs to Windows XP Professional for this exact reason. I pop some newly acquired Windows XP Professional with SP3 "Get Genuine" media (designed for those folks that have potentially illegitimate Windows versions); the upgrade is going well until ... the part where I enter the license key. It won't take it, even though I know it's valid (tested against an XP Home machine in the same office).
While trying to find a reason why I can't upgrade, I stumble upon another blog with some basic instructions on how to join XP MCE to a domain. The first step the author lists is to install the Windows XP Recovery Console; I run the command and restart ... and ... bluescreen.
I turn to my trusty recovery tools disc (which has gotten me out of more tight spots than you can imagine) and boot to a WinPE shell which has a bunch of great tools loaded, including RegEdit PE.
To perform this feat of amazement yourself:
1. From a WinPE installation, launch RegEdit PE, point it to the Windows installation director, and load up the registry hives.
2. Navigate to HKEY_LOCAL_MACHINE\_REMOTE_SYSTEM\WPA\MedCtrUpg.
3. Double-click the value IsLegacyMCE.
4. Change the '0' to a '1'.
5. Close RegEdit PE and restart the machine into Windows.
6. Join domain.