I wasn't actually aware there was more than one version, code-wise. I'm guessing that the 95/98 one does actually work normally on XP, and if not then it almost certainly will with the help of ScummVM.
I'm very saddened to have lost my original CDs (only have the box and manual) so I can't verify the original 1997 version does actually work on XP, although I don't think I've seen many people saying it doesn't.
Incidentally, anyone know if a patch was ever released for CMI? I can't remember at all.