If the version of Windows XP that you want to install was shipped with the other system,
it's an OEM version of Windows XP, and is illegal to install on any other system. Nor is
it legal to install Windows XP from one license onto two running systems. Nor would the
product key for one CD work for installing from another CD. Also, laptops have much
proprietary hardware, and it is not advisable to install the operating system and drivers
from any other media than what came with that laptop's OEM version of Windows XP. I'm
assuming that if your laptop didn't come with a Windows XP CD, that the install files are
on a hidden partition, and that you either can't reinstall from those files, or don't want
to. Your best bet is to get with the maker of the laptop, and ask for media to reinstall
Windows XP. Many companies, which didn't originally supply CDs have changed their
policies about shipping the CDs to customers who ask for them. A lesson: Don't ever
purchase a Desktop or Laptop that doesn't come with a Windows XP CD. Depending on
reinstalling from hidden partition files is problematic, and System Recovery disks have
their limitations.