1. Make sure you are not using auto-mounting
2. Plug in device and in a root terminal type fdisk -l or fdisk.distib -l or blkid to find out what your usb devices shows up as. Mine shows /dev/sdc1
3. Open a root terminal and simply type

new_usb.sh path_to_iso file.file_name.iso usb device path -b grub

where b=bootloader, options =grub (recommended ext2/3/4 or fat), or ext (extlinux for fat32) or iso (isolinux).

Real example on my box.
Code:
new_usb.sh /media/sda3/remasters/antiX-base/antiX-base-test1.iso /dev/sdc -b grub


This info is from a pm anti sent me.