I got a 23 inch 1920x1080 LCD screen for my laptop... AND... I got it working under Ubuntu (and Kubuntu)!
Here are the steps -
1) Edit your xorg.conf to change the virtual mode line
sudo kate /etc/X11/xorg.conf
Virtual 2560 1024
Virtual 1920 1880
2) Add appropriate mode lines to your ~/.bashrc
sudo kate ~/.bashrc
Add the following lines at the end -
# Mode lines for external LCD 1920x1080
xrandr --newmode "1920x1080" 172.80 1920 2040 2248 2576 10801081 1084 1118 -HSync +Vsync
xrandr --addmode VGA 1920x1080
xrandr --output VGA --mode 1920x1080
3) Reboot the system (Somehow logout and login did not work for me). Or if you have had it enabled, press Ctrl-Alt-Backspace to restart the x.org server.
Rant: WHY OH WHY does KDE not have an option to extend your desktop across multiple screens?? I can do it easily in Gnome, but all KDE can do is mirror your desktop which sucks when the screens differ greatly in reolution.