Do you know which directory you downloaded the Gateway and Workstation images into? If you did not download them into /home/user_name the command will not work.
If this is the problem you can:
cd /path/to/Whonix_images
tar -xvf Whonix-Gateway-*.libvirt.xz tar -xvf Whonix-Workstation-*.libvirt.xz
Shoot, I have no idea how to fix that. I’m using Trisquel as it seems to be the most functional libre OS and was hoping to use Whonix with it. Any ideas/suggestions?