Create an ISO file from the XP installation CD and use MultibootISO
to create a bootable USB flash drive. Copy your XP ISO file to the USB flash drive. There is a file called "menu.lst" on the root of the USB flash drive. Open it up in a text editor and add the following entry:
title XP installer (or whatever you want to name it)
find --set-root /XPinstaller.iso (put the actual name of the ISO file you are using)
map /XPinstaller.iso (hd32)
Give it a try and let me know how it works out.