Sorry, but that's completely wrong. Windows XP is built on the Windows 2000 and NT architectures, not based on the Windows 98/95 codebase, although "the best features of Microsoft's consumer operating systems" are apparently merged in.

Microsoft themselves explain this on their "Features" pages: Home Edition/Professional Edition, and probably in more depth in some KB article or on MSDN somewhere, but I don't have time to go digging.

Interestingly, a previous employer of mine used to ask the difference between 98 and XP as a part of their interview procedure - it's surprising how many candidates with "Expert: Windows 95/98/Me/2000/XP" on their CV got it wrong ...