If you are wanting to reformat and reload windows then you an perform a reformat as part of the install.
Put your xp disk in the drive and power up your machine Hit enter when prompted to boot from your CD.at the menu that will appear after a few minutes press enter to install a new copy of Windows then press F8 to accept the licence then when promptd pick the place you want to install and delete the partition by pressing "D". You will then be prompted to create a new partition in the empty space. This will remove all data from the deleted space.and just follow the instructions to finish.
Hope this helps and if you need anything else just ask.
So you want to upgrade or do you want to do a complete install?
Let me know