I have to admit I am totally confused here.
You're computer that came with no OS now has XP installed.
The first thing you did was install a game.
You didn't update Windows first?
You didn't install an AV first?
Where did you say you got this computer?
Where did you buy XP?
Where did you buy this game?
Once you installed this XP version did you also install the the drivers for this particular model?
It seems to me that a a proper XP install and updates as well as security should be your first concern. Gaming is the least of your worries.