Most of the following taken from : http://www.msfn.org/board/topic/151992-install-xp-from-usb-without-extra-tools/, just modified to include syslinux support.

Let me know if there are any omissions; it an XP installer bluescreens on boot for me so I can’t actually test.

1. Obtain an XP iso file
2. Format drive with one FAT parition, marked bootable.

3. syslinux -i /dev/sdXX
   

4. $ cp /usr/lib/syslinux/bios/mbr.bin >/dev/sdX
   

5. $ mount /dev/sdXX /mnt
   

6. mkdir /tmp/xp_iso
   mount xp.iso /tmp/xp_iso
   cp -ar /tmp/xp_iso/* /mnt
   umount /tmp/xp_iso
   rmdir xp_iso
   

7. cp /usr/lib/syslinux/bios/{chain.c32,libutil.c32,menu.c32,libcom.c32} /mnt
   

8. cp /mnt/I386/{NTDETECT.COM,SETUPLDR.BIN,TXTSETUP.SIF} /mnt
   

9. Edit /mnt/syslinux.cfg:

   UI menu.c32# Windows XP
   LABEL windows_xp
   MENU LABEL Run Windows ^XP Setup
   COM32 chain.c32
   APPEND fs ntldr=SETUPLDR.BIN
   

10. umount /mnt
    

11. Boot from the USB stick