Usually Ubuntu and all of its derivatives would recognize an external monitor and set it up reasonable automatically. At least all the flavours I tried of Ubuntu, Xubuntu, Linux Mint did that – with Linux Mint most ellegantly – in my opinion.
I read some warnings that one should be prepared for “regressions” in connection with some development issues in Karmic Koala.
So:
Second (external) display does not work as used to anymore. After Xubuntu Karmic Koala fresh install I found just “Display1” in the Display settings. I could set it to the (higher) resolution 1280×1024 of the external display, but then my Lenovo X61s laptop display (1024×768) would turn black.
A workaround was not so hard though:
xrandr
in the command line showed that both the laptop display (“LVDS1”) and the external display (“VGA1”) were detected and running; just that the external display was running at laptop resolution too.
Xrandr did even detect the optimal settings for the external display.
Thus
xrandr --output VGA1 --auto --above LVDS1
set the resolution and refresh rate of the external monitor correctly and put it as an extended Desktop “above” the laptop screen. Exactly the way I did like it in Linux Mint 7 before…
Xrandr is commandline interface “to set the size, orientation and/or reflection of the outputs for a screen” (from the man page).
In Ubuntu
man xrandr gives a short description with examples. I derived my workaround from one of the examples given.
Rforge 