Forcing external VGA monitor resolution

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http://forums.fedoraforum.org – I have a Sony Vaio laptop running F17/KDE4.9, with Intel Mobile GM965/GL960 graphics. Laptop display resolution is 1280x800. I connect a new ACER 1920x1080 external monitor via VGA cable (no other socket on laptop) hoping to have the option of using it at native resolution but am only offered 1280x800. How can I get the correct resolution offered in the Display Settings GUI? I've dabbled with xrandr after reading other's troubles but with no success but that may be because I don't really understand command line syntax etc. Am I missing something obvious here, I really did think Fedora was m (HowTos)