enter BIOS ( Setup ) and set the first boot device as CD/ROM. Put your XP Disc in the drive and disconnect all external peripherals except the monitor, keyboard and mouse, and be sure those are not USB, or wireless. Any internal USB card should also be removed.
Once you set your BIOS to boot first from cd . . when it restarts you will see a black screen with a prompt "Press any key to boot from CD
" . . do that and you will be able to delete any or all partitions and recreate one or more, then proceed to formating and installing XP.
That message can pass quickly, so have a finger on the keyboard when you boot. This will delete all data on the drive
so be sure you have your important data backed up. The prompt will appear after every reboot, but do not press any key on subsequent reboots. The setup process will continue with no action required from you.
If you do not get that message, and you have another optical drive, try the XP CD in the other drive.
If you are installing on SATA drive, there is an additional step:
This is a site that walks you thru a simulated XP installation:
These are good guides to reinstalling XP . . you might want to print one for reference during the install.
You will likely have to reload drivers (Chipset first) and applications, If your XP installation disc does not include SP2, after the installation, you will need to download and install SP-2, while windows is clean. Prior to connecting to the internet be sure you enable the XP firewall.
If you want to save your files and settings, you can use the XP Files and Settings Transfer (FAST) wizard to create an image of them and save to cd or other removable media. These are good guides to using the FAST wizard. Just be sure you have an up-to-date antivirus before you re-instate them!
For help entering BIOS: http://www.michaelstevenstech.com/bios_manufacturer.htm