From https://wiki.ubuntu.com/HardwareSupp...nesLaptopsAcer

Section on Acer 5612WLMi (which is the closest number I can find)...

X resolution is 1024x678 but in Xorg.conf file there is 1280x800 resolution. And it should be 1280x800 that is the real screen resolution. This bug is solved with the 915resolution program: http://www.geocities.com/stomljen/ (a link to ubuntu wiki is here)
Full information here.

Worth a look?