You need loram.

Others have had trouble installing without cd and trying to boot from usb. There was a lot of information on the old forum.

Some options-

Boot from online, which seems to allow loram, especially if you have high-speed internet ( http://boot.slitaz.org/ ).
Use an external cd.
Use an external hd.
Use a zip drive.
Install a micro linux that fits on a few floppies and allows you to copy slitaz onto the hd from somewhere else.
Use a lan connected to a better computer.
Remove hd and connect it to a better computer to install slitaz on the removed hd.