Shoutbox

Format the hard drive if you haven't already:

Right-click My Computer > Manage > Storage > Disk Management > Right-click hard drive and select Format (make sure you choose the right drive).. If you want a quick format just select Quick Format.

(You can also format it by booting up from the Windows XP disc).

I just re-read your question and it seems as though you are installing it on a new system (therefore not having any hdd's with Windows XP on them). So you'll have to format it after booting up from the Windows XP CD.

Install Windows XP:

Boot up from the Windows XP CD (If you're computer doesn't check automatically then you have to enter the BIOS by pressing the DEL button (usually) when you turn on your computer).. and finding the boot-up options change the first boot-up device to CD-ROM.

Save & Exit. (make sure you don't touch anything else because you can seriously screw up your computer by fiddling around in here).

Make sure your Windows XP CD is in the CD-ROM drive once you restart your computer and follow the prompts.... then install Windows XP onto your preferred drive.