Change the bios to boot from CD/DVD first, then hard drive. Install the XP install CD and boot from it. When you get to the section that allows you to add/delete/create partitions, delete all partitions and create a new one for XP. Now continue the installation. If the laptop uses sata drives, you will need the sata drivers on floppy disk. You will also need all necessary motherborad and other hardware drivers to install.
If you aren't familiar with the process, I'd have a friend or someone help you.