Hi adamf,
To use the Graphics Installer, you will have to upgrade to the latest version of Ubuntu which is 13.04.
In general, however, you will have to dive into Ubuntu's display settings. Some desktop environments attempt to find a "common" resolution across displays. Consult Ubuntu's documentation for how to "extend" your desktop across multiple displays so you can utilize your external monitor's highest resolution.
Cheers, hope that helps
Ubuntu will only allow 1024x768 or 800x600 resolution options for my external monitor, an HP 2159m (which supports 1920x1080). The laptop's built-in monitor works fine.
I'm running Ubuntu 12.04 and my graphics card is an Intel HD 4000.
Do I need to update the drivers? Can someone point me in the right direction?
Many thanks