Problem with the soundcard

Good morning everybody,
First of all i wanna apologize for my english, i bet nobody will understand me so i will try my best to talk as possable as i can.

my pc performance is :-
Processor : intel pentium 4 531 3.00GHz ~2CPUs.
Memory : 2gb of rams 1x1.
GPU : Nividia geforce 210 1gb ddr3 .
OS : Windows xp professional version 2002 sp3
i dont know about my soundcard but the problem comes with it.

some games such as Grand theft auto san andreas
i am comfortable with the FPS (FramesPerSecond).
i can say that its stable.
but when i shoot m4 or mp5 or anything makes alot of noise
my fps drops -10 / -15.
i tried installing windows 7 by extracting the .iso file and install it directly
i know its wrong  
i liked windows 7 cause it didnt makes the lags or FPS' drops.
but windows 7 is very heavy in games. im not comfortable with it
so what the hell is wrong with the xp
BTW, my soundcard manager is Realtek v6201

please answer me as soon as possable