If you really need the abilities of XP Pro, I'd be wary of doing this. It might work for now, but who knows when Microsoft might break this hack. I'm also a little wary, as if it was really never anything more than a registry key entry, I would think Microsoft wouldn't have gone to the trouble to disable the XP Pro features. My guess is that some of the more esoteric XP Pro features are totally broken by MCE, and Microsoft doesn't believe users who want MCE will ever need the domain features in XP Pro. So they didn't write the code to fix the issues, they just disabled the features.