naveen is completely correct
i would like to add that while installing XP make sure you choose the option for a new installation and not for an upgrade
it is always better to install different os on different partitons so if you dont have more than one partition use partition magic to make new partititon for Windows XP or if your harddisk is completely clean then you can even use fdisk utility of MSDos, i will say get someone who has information on such topic while installation