SOLVED: nulock ON before logging in

[Paul Varjak]

Finally I solved it as follows:

sudo apt-get install numlockx

Edit the file /etc/kde3/kdm/Xsetup adding:

# Activate numlock before log in
if [ -x /usr/bin/numlockx ]; then
 /usr/bin/numlockx on
fi

The problem is that (I think) this change can be lost when updating
kde or Xserver, but I'm not sure.

Thanks to everybody for the help.
Paul.