I will say that mine are ISO's from a Microsoft online repository.
I'm obviously not including the license keys, and there are situations where OEM licenses will not work with MS-originated discs. I can't remember if there are 3 classes of license keys or only 2, but it's either OEM/MS, or OEM/Retail/MS...
It might be best to obtain the Dell discs above as a backup in case mine don't work for you. If you're working off of a set of OEM licenses, it's possible that my discs won't work.
Of course, WinXP-MCE was a pretty small release in the marketplace and there may only be one licensing scheme for it at all.