Windows XP only?

I have an unusual problem. My relatively new laptop (Winbook J4) came with Windows XP pro. After awhile it became extremely slow, nothing seemed to work properly. It is a Pentium IV, 2.4GHZ and my old Dell (Pentium III-500) seems to work faster. I decided to replace Windows XP Pro with Windows 2000 Pro. There wasn't much improvement. Winbook technical support claims that the computer was designed for XP only and will not work properly with Windows 2000. I have problems believing this.
Any thoughts?

Thanks Triple7's, I think that I will give Windows XP another chance. Several computer experts suggested to do just that.
You are correct, Winbook is very sluggish compared to other laptops, it was a disappointment all around.