why did u started this again, anyway, lemem clear you out,
once you get bootable winXP cd., it'll give you option in start, like, where to install your windows, and in case if it finds a pre-installed windows, which It will, then it'll ask for weather to repair it or clean install. which of course is ur choice. and it'll format your hard drive as wll prior to install O/S Files
got it?