I also have a Latitude C840 with the Geforce4 400 Go. I was able to make my display work properly by using the nvidia-glx-legacy packages.
I also had to add the following in /etc/X11/xorg.conf to make anything GL run reasonably well. Section "Extensions" Option "Composite" "Disable" EndSection -- [feisty] X is blank after upgrade https://launchpad.net/bugs/82312 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
