I think there are many minor differences, since both are internally Windows NT 5.x, and one can be the best for some people while the other can be the best for some other people. It depends on what you may need.
Some of the differences are:
- Windows 2k has lower system requirements.
- Win 2k has no product activation.
- If you have enough resources, Win XP could be a little faster.
- I think the security has been improved in XP (windows firewall, etc…)
- If you look for drivers for new hardware, I think you will find it more easily for Win XP.
Hope this helps.
Onother important difference is that XP has more hardware drivers available out of the box than Windows 2000 did. I am also pretty sure that there was not a 64-bit version of Windows 2000 Professional, but there is a 64-bit version of XP.
If you are considering using wireless networking then you should definitely go with XP. Windows 2000 was created when wireless networking was in its infancy, and consequently XP has much better wireless support.