If you just want to wipe the drive and start over, boot off the XP setup disk, when it gets to the partition selection, delete the existing partition. Then format it (quick is OK), and continue with the setup. The drive will be cleaned out and you can then install XP.
Make sure that you have the COA number to hand, you will also need to download and store on a flash drive or external harddrive the motherboard drivers unless of course you have a motherboard driver disk.
You will also need to download the latest driver for your graphics card.