Depends on how old the computer is ... .. if you want to install XP. You should have at least 128MB RAM otherwise it will be slow.
If your laptop is PII or PIII then install windows XP shouldn't be a problem, you just need to find the right driver. Most of the time you should be able to use windows nt or windows 2000 drivers for XP if XP didn't already pick up your driver.
I have installed Windows XP on Asus M8300 (PII 366 + 192MB RAM + 6G HD)