If you for some reason (as the 4 Gb file size limit of vfat) want to have a live usb on a ntfs filesystem you can use the grub2 bootloader. I write how i did it until i can (almost) remember:
start the pc from the slitaz cd (or iso in virtualbox)
as root mount your ntfs partition under /boot. your partition could be different from sda1 if you have more than one disk, so be very careful about what you type on the keyboard.

mkdir /boot
mount /dev/sda1 /boot

then remove grub and install grub2

tazpkg remove grub
tazpkg get-install grub2 

now install grub2 in your MBR

grub-install --no-floppy /dev/sda

if you got a "embedding area too small ..." error read this http://osdir.com/ml/grub-devel-gnu/2010-01/msg00287.html and leave some free space before your first partition. i left 1 Mb but probably i've been a lot abundant. now create a grub.cfg file in /boot/grub/ and put this inside it:

set timeout=5

set default=0

# (0) Slitaz
menuentry "Slitaz" {
#insmod ntfs
set root=(hd0,1)
linux /boot/bzImage root=/dev/null lang=it_IT kmap=it rw vga=normal autologin
initrd /boot/rootfs.gz
}

change the options in the linux line to reflect your needs.
now you could reboot if it wasn't because i forgot to do a tazusb gen-liveusb in the start. if you do it now then you must reinstall grub2 in your mbr because slitaz would install another bootloader wich does not work with ntfs, so i did this:

mount /dev/cdrom /media/cdrom
mkdir /boot/boot
cp /media/cdrom/boot/bzImage /boot/boot/
cp /media/cdrom/boot/rootfs.gz /boot/boot/
sync
reboot

good luck