Fortunately, looking for Internet I could find a solution. In the first case it's enough to add this lines at the end of /etc/X11/xorg.cong file:
Section "ServerFlags"
Option "DontZap" "False"
EndSection
To avoid that update manager appears whenever it likes just type this in a terminal:
gconftool -s --type bool /apps/update-notifier/auto_launch false
I have also some problem with the 3D acceleration of my card, a Intel 945GM, that was fixed downgrading the driver to the intrepid version. For that, I added these lines to /etc/apt/sources.list:
deb http://ppa.launchpad.net/siretart/ppa/ubuntu jaunty main
deb-src http://ppa.launchpad.net/siretart/ppa/ubuntu jaunty main
and doing
apt-get update
and sudo apt-get install xserver-xorg-video-intel
.The moral of the post is that Human Beings are prisoners of our habits.