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.
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:
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.
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).
man xrandr gives a short description with examples. I derived my workaround from one of the examples given.