Driver reinstallation after every reboot

hey guy, needing a little help here. my brother had just installed windows XP on his new computer FROM windows vista and ive had to find drivers that are compatible with xp. ive found them all and installed them all and the computer now works fine... untill i need to restart the computer then all drivers i had just installed need to be reinstalled and im stumped as to why.
i dont really have a great knowledge of computers so some help would be much appreciated.

OS: windows xp sp2
drivers that need reinstallation: NVIDIA geforce 6200
realtek di def audio
intel pro/100v network connection
USB controllers

Any help would be great, if more info is needed just let me know what.
Cheers, Peety

Edit: this is the computer specs, other than the video card: http://h10025.www1.hp.com/ewfrf/wc/...s=228&product=3339276&dest_page=documentIndex