The reason xp was created was because it is the most secure and stable version of windows ever written. and it is getting better all of the time.
I had to abstain from voting on this one -- jumped straight from 98SE to XP simply because XP was all that was available on new systems here when my old mobo died of old age last year. What I miss most about 98SE (and my apologies for this being a little off-topic with regard to 2K vs. XP) was its ability to handle quite a few DOS programs, often nicely running even some fairly demanding ones in DOS windows without having to reboot.
My HD's throughput speed is faster with XP. That said, I would go with W2K in a split second if I should decide to get an ATA controller card (bypasses the IDE).