Answering my own post, for it may help someone in the future

The partition to which I initially tried to install was in
the upper 10Gb of a 80Gb HD. It seems this was the cause of
the problem. When I managed to free disk space lower (towards
15 GB), the installation "just worked"! I don't know if lilo
is to blame but apparently the knoppix installer (Fabian's
in my case) is not repsonsible. Go figure...