1. Set your PC to boot from CD.
2. A message will appear asking you to press a key to boot from CD.
3. Press key and wait for the file-loading to finish.
4. Select 'install windows'
5. Select location to install.
6. select to delete partition / format the location
7. install XP as normal.

Try this link. It has piccys of the steps too.

http://www.theeldergeek.com/xp_home_..._-_graphic.htm

Just remember to format the location where you are installing XP to NTFS