Edmond, if it hasn't been mentioned I would recommend Vietcong. It a great FPS for XP. I wish GOG would release a version of this game for Win 10. But that seems to be a pipe dream for a while now no matter how many people wishlist it. Who knows maybe its in the works. But in any event you may want to try Vietcong for XP.

https://www.gog.com/wishlist/games/vietcong