Which version 

ftp://ftp.slax.org/SLAX-6.x/rc3/README.usb-iso

If you need both TAR version (for your USB drive) and ISO version (for CD), you don't have to download both.

Here is how to convert it from one to another:

If you downloaded ISO file and you wish to convert it to TAR version

If you downloaded TAR file and you'd like to generate ISO