Xp is even easier than that
Ok set your BIOS to boot from the CD rom as the first boot device.
Stick your XP cd in the CD rom and it will ask you where you want to install it as it will detect that there is already an installation of XP on the drive.
Select the same partition and it will say something about its not recommeneded, click next and then it will give you the option to format it.
Select which type of format you want, Fat32 or NTFS, it will only give you that option if the drive or partition that you are installing to is 32 gig or less.
It will allow you to select the size of partition too, if you want to resize it or create another partition.
If you do create another partition then once XP is up and running go to the Disk Management again and select the other partition/s and right click and select format