I've just tried to boot from the internet via the grub4dos floppy.
It fails saying it can't find http://boot.slitaz.org/gpxe .
Indeed this file doesn't exist; but http://mirror.slitaz.org/boot/gpxe does. Maybe the floppy image needs to be updated? (Did the server directory tree change recently?)
(I looked into the floppy image but couldn't find a hardcoded address; otherwise I would have tried to change it.)
edit: OK, just figured out I should try the second GPXE entry in the GRUB menu! It works... Still, the problem I encountered with the first entry looks strange.