Answer: It is not possible to set the display resolution to 1366x768 in a Acer Aspire One ZG5. The Acer Aspire One ZG5 does not support resolutions higher than 1024x600.

As you have 1280x768 listed under System Settings > Displays, it is very likely you do not have an Acer Apsire One ZG5. Ubuntu 12.04 will correctly detect the display's native resolutions and populate the settings appropriately during installation.

Source: http://support.acer.com/acerpanam/netbook/0000/Acer/AspireOneAOA150/AspireOneAOA150sp2.shtml