Help... I am looking into dumping my hard drive because of viruses and reinstalling windows xp I

Question

I am looking into dumping my hard drive because of viruses and reinstalling windows xp I don't need to save anything just want to start fresh... I have a HP Pavillion 7917 and I am not sure how to doit... Thanks... I know that staples does it but they charge an arm and a leg.... I know with some Help I can do it...