Installing Salix from a USB key is also possible. You can use dd to transfer the contents of the Salix iso image to your USB stick, using a command line like this:
dd if=salix_image_file.iso of=/dev/sdb
Of course, you'll have to replace salix_image_file.iso with the exact path and name to the iso file you would like to use.
sudo fdisk -l. If you are not 100% certain, then do not proceed as this could permanently destroy the contents of an entire hard drive.
After writing the iso image to your USB stick and setting your BIOS to boot from it, the installer works exactly as described above when booting from a CDROM. The only difference is that when you are asked for the medium to use as a source for the packages installation, you should select the "Install from a Salix USB" option.