Microsoft Word is not part of Windows regardless of which version. It may have been preinstalled as an extra on your pc.
You can't uninstall it and have it go back to XP. It would require complete reinstalation of XP after formatting the drive.
You would need an XP instalation disk, or a restore disk from the maker of your pc. If you have an Microsoft XP disk, it won't contain Word, If it's a makers restore disk then you should have all the programs you had when new.
Without a restore disk you would also need the XP drivers for your hardware if you are using a Microsoft XP instalation disk.
Why not give yourself a chance to learn how to use it. Once you get used to it you won't want to go back.
In any case you will find it a lot easier then reinstalling from scratch.
An alternative to Word that is compatible is Open Office, you can dowload it for free: http://www.softpedia.com/get/Office-tools/Office-suites...
Or, get OpenOffice. It's free and it's not too bad with most normal documents from Microsoft Office.
More than likely, I'm assuming you have a PC that came preloaded with XP. It might have also come loaded up with an OEM copy of Office which means more than likely, it will only work with the XP install unless it came with it's own install disc.
If you can't find it and don't want to pay for a new copy of Office, then do as I suggested and get Openoffice. You can go to http://www.OpenOffice.org and download it from there. It's free, and I mean free. No nagware, no strings attached, etc.