You may be able to install word 97, and run it in compatibility mode. I honestly don't know, but I suggest you install open office, which does the same and more, and it's free.
I have used vista since it came out, and would not go back to xp..
apart from anything else, as it's a new computer, the drivers, and various other things may not suit XP, and could cause even more problems.
All the best.