It is very easy to install Windows XP from USB. Here are the steps how.
- Rip an ISO of your Windows CD or DVD. For this I recommend Alex Fienmann's excellent ISO Recorder software.
- "Burn" the ISO to a USB stick with Rufus.
- Safely Eject the device from your computer, put it in your target computer and boot from it.
- Run through the install as if you normally would if you had booted from the original disc except now it should be faster.