I've got both running in front of me right now. Windows XP Pro uses fewer resources on my system (1.2 GHz, 512MB Dell Inspiron 8100) and is a bit more stable than a similar system (IBM A21 1.2GHz, 512MB) loaded with Windows 2000.
I'm running pretty much the same workload on each and I'm seeing better performance and better resource allocation on the XP side of the house.