Setting up Windows XP on a USB drive
Setting up Windows XP on a USB drive
Consider using an SD card to SATA adapter instead. Install it and connect the SD card to a USB-to-SATA converter.
The issue isn't about installing OS on a flash drive, but starting it on various computers. Modern hardware lacks XP drivers, and adding them would be impractical.
OP intends to put the operating system on a USB stick instead of making a separate installer.
Watch the YouTube tutorial that explains the process in detail.