I have the same problem on old Debian Lenny seedbox, after just few restarts after insallation. Both in multiuser and singleuser modes it hangs after checking root filesystem and line "Clearing up ifupdown...", but echoes keyboard presses. Ctrl-C doesnt do a trick, hardware reset doesnt help too. My kernel & ifupdown are the default ones from installation, root filesystem is reiserfs. Hardware is : Coppermine-based Celeron 1GHz, 384M of RAM, 3 net interfaces: two are RTL8139-based, and VIA Rhine III (which gets its address from dhcp, other are static).
>Numlock not working ... however keyboard echoes on screen . The same thing.
