Assuming that you have MS-XP-OEM preinstalled with Recovery Disks, it is a lengthy and messy job. Go the the web site of your OEM supplier, and they will usually carry full instructions for re-installation. Make sure your follow all instructions or you could loose everything you have on your HDD.
BTW, there is going to be an article on how to clone your HDD in next month's mag, PCA. It might help.