Just put in the discs given and follow the instructions on
screen.
If you have a Windows CD of your own, go into BIOS, set the first
boot device to the CD drive. Put in the XP CD, save the settings
and Windows will now prompt you to reformat.
When Windows detect a previous installation of Windows, select the
Format option to format the whole C drive before installing XP,
otherwise, you may face problems with Windows or it will dual boot
each time you start your PC.