Windows XP is newer than Windows 2000, so now more software is more compatible with XP over 2000, however. Windows XP is a much slower operating system compared to Windows 2000 for a number of reasons. The same applies to why Windows 98 is slower than Windows 95, the same reason is to why Windows XP is slower than Windows 2000 and Microsoft was stupid not to announce that XP is slower than Windows 2000 and state that Windows XP is better than 2000, which is why its slower. However, Windows XP would be almost the same speed, maybe even faster on a new computer compared to Windows 2000.
Windows 2000 also is mostly for business users over home users, which makes it a better OS from XP, but you can easily install the stuff which would make 2000 like a home OS, which in my opinion would be better than using Windows XP Home Edition which is Windows 2000 not having ANY business features, plus on the same kernel as Windows NT, the business OS, which I believe is Irony, since NT is for business, plus the slowness of XP.