1. In Linux environment, under the directory which contains usbboot.img

$ cat /proc/partitions
major minor  #blocks  name

  8     0  156290904 sda
  8     1   77152131 sda1
  8     2    9896040 sda2
  8     3   67384642 sda3
  8     4    1855507 sda4
  7     0     194322 loop0
  8    32    2000880 sdc    <-------- USB Device
  8    33     883543 sdc1
  8    34     104422 sdc2
  8    35     883575 sdc3

$ dd if=usbboot.img of=/dev/sdc bs=1024 count=1900000 $ sync

2. Plug the USB drive to the target, reboot target and press F11 for its
BIOS.
   Please eelect boot from usb hard disk and have fun.

Note.

The partition layout is

+----------------------+
 |     FAT 32              |    sdX1     862M
+----------------------+
 |     Kernel              |     sdX2     99 M
+----------------------+
 |     RootFS             |     sdX3     850M
+----------------------+

You may access the first partition from a Windows PC.
Load the image files there.