Go to the link below, HP's support site, on that page type in pavilion and the model number of your pc, on the front of the case it will say pavilion and some number will be next to it with possible letters like x, a, c and a few other possibles. After searching for your model it should ask what operating system, click XP and you should find the right sound driver on that page.
http://welcome.hp.com/country/us/en/support.html