If you have the original installation media that came with the laptop you could pop in the Windows XP reinstall disk and perform a clean installation that will wipe data from the disk.
Your best solution would be to download this https://dban.org/blancco-drive-eraser/ disc image and burn to a CD or DVD using the program image burn at https://www.imgburn.com/ when you boot this in your laptop it will offer to wipe the disk.
Alternatively you could remove the Hard drive from the laptop and keep it as an archive copy of your data with an external enclosure.