>>Покажите xorg.conf
>
>Собственно вот. Из Mandriva 2006
>
># File generated by XFdrake.
>
># **********************************************************************
># Refer to the XF86Config man page for details about the format
>of
># this file.
># **********************************************************************
>
>Section "Files"
>    # Multiple FontPath entries are allowed (they are
>concatenated together)
>    # By default, Mandrake 6.0 and later now
>use a font server independent of
>    # the X server to render fonts.
>    FontPath "unix/:-1"
>EndSection
>
>Section "ServerFlags"
>    #DontZap # disable <Crtl><Alt><BS> (server abort)
>    AllowMouseOpenFail # allows the server to start up
>even if the mouse does not work
>    #DontZoom # disable <Crtl><Alt><KP_+>/<KP_-> (resolution switching)
>EndSection
>
>Section "Module"
>    Load "dbe" # Double-Buffering Extension
>    Load "v4l" # Video for Linux
>    Load "extmod"
>    Load "type1"
>    Load "freetype"
>    Load "synaptics"
>    Load "glx" # 3D layer
>    Load "dri" # direct rendering
>EndSection
>
>Section "InputDevice"
>    Identifier "Keyboard1"
>    Driver "keyboard"
>    Option "XkbModel" "pc105"
>    Option "XkbLayout" "us,ru(winkeys)"
>    Option "XkbOptions" "grp:alt_shift_toggle,grp_led:scroll,compose:rwin"
>EndSection
>
>Section "InputDevice"
>    Identifier "Mouse1"
>    Driver "mouse"
>    Option "Protocol" "ExplorerPS/2"
>    Option "Device" "/dev/mouse"
>    Option "ZAxisMapping" "6 7"
>EndSection
>
>Section "InputDevice"
>    Identifier "SynapticsMouse1"
>    Driver "synaptics"
>    Option "Protocol" "auto-dev"
>    Option "Device" "/dev/input/mice"
>    Option "MinSpeed" "0.09"
>    Option "MaxSpeed" "0.18"
>    Option "BottomEdge" "4200"
>    Option "SHMConfig" "on"
>    Option "FingerLow" "25"
>    Option "LeftEdge" "1700"
>    Option "MaxTapMove" "220"
>    Option "MaxTapTime" "180"
>    Option "FingerHigh" "30"
>    Option "VertScrollDelta" "100"
>    Option "TopEdge" "1700"
>    Option "AccelFactor" "0.0015"
>    Option "RightEdge" "5300"
>EndSection
>
>Section "Monitor"
>    Identifier "monitor1"
>    VendorName "Generic"
>    ModelName "Flat Panel 1280x800"
>    HorizSync 31.5-90
>    VertRefresh 60
>
>    # 1280x800 @ 60.00 Hz (GTF) hsync: 49.68
>kHz; pclk: 83.46 MHz
>    Modeline "1280x800_60.00"  83.46  1280 1344 1480
>1680  800 801 804 828  -HSync +Vsync
>
>    # TV fullscreen mode or DVD fullscreen output.
>
>    # 768x576 @ 79 Hz, 50 kHz hsync
>
>    ModeLine "768x576"     50.00  
>768  832  846 1000   576  590
> 595  630
>
>    # 768x576 @ 100 Hz, 61.6 kHz hsync
>
>    ModeLine "768x576"     63.07  
>768  800  960 1024   576  578
> 590  616
>
>    # modeline generated by gtf(1) [handled by XFdrake]
>
>    ModeLine "1280x800_120"  181.21  1280 1376 1520
>1760  800 801 804 858  -HSync +Vsync
>
>    # modeline generated by gtf(1) [handled by XFdrake]
>
>    ModeLine "1280x800_100"  147.89  1280 1376 1512
>1744  800 801 804 848  -HSync +Vsync
>
>    # modeline generated by gtf(1) [handled by XFdrake]
>
>    ModeLine "1280x800_85"  123.38  1280 1368 1504
>1728  800 801 804 840  -HSync +Vsync
>
>    # modeline generated by gtf(1) [handled by XFdrake]
>
>    ModeLine "1280x800_75"  107.21  1280 1360 1496
>1712  800 801 804 835  -HSync +Vsync
>
>    # modeline generated by gtf(1) [handled by XFdrake]
>
>    ModeLine "1280x800_60"  83.46  1280 1344 1480
>1680  800 801 804 828  -HSync +Vsync
>
>    # modeline generated by gtf(1) [handled by XFdrake]
>
>    ModeLine "1280x800_50"  68.56  1280 1336 1472
>1664  800 801 804 824  -HSync +Vsync
>EndSection
>
>Section "Device"
>    Identifier "device1"
>    VendorName "Intel Corp."
>    BoardName "Intel 915"
>    Driver "i810"
>    Option "DPMS"
>EndSection
>
>Section "Screen"
>    Identifier "screen1"
>    Device "device1"
>    Monitor "monitor1"
>    DefaultColorDepth 24
>
>    Subsection "Display"
>        Depth 8
>        Virtual 1280 800
>    EndSubsection
>
>    Subsection "Display"
>        Depth 15
>        Virtual 1280 800
>    EndSubsection
>
>    Subsection "Display"
>        Depth 16
>        Virtual 1280 800
>    EndSubsection
>
>    Subsection "Display"
>        Depth 24
>        Virtual 1280 800
>    EndSubsection
>EndSection
>
>Section "ServerLayout"
>    Identifier "layout1"
>    InputDevice "Keyboard1" "CoreKeyboard"
>    InputDevice "Mouse1" "CorePointer"
>    InputDevice "SynapticsMouse1" "AlwaysCore"
>    Screen "screen1"
>EndSection

В Subsection "Display" попробуйте добавить строчку следующего содержания:

Modes "1280x800_60"

Вот кусок из моего конфига, но другого ACER-a (настраивал давно и не помню что к чему):

Section "Device"
Identifier "Intel Corporation Mobile Integrated Graphics Controller"
Driver "i810"
BusID "PCI:0:2:0"
Option "XAANoOffscreenPixmaps" "true"
Option "ForceBIOS" "1024×768=1280×800"
EndSection

Section "Monitor"
Identifier "Generic Monitor"
Option "DPMS"
HorizSync 28-64
VertRefresh 43-60
EndSection

Section "Screen"
Identifier "Default Screen"
Device "Intel Corporation Mobile Integrated Graphics Controller"
Monitor "Generic Monitor"
DefaultDepth 24
SubSection "Display"
Depth 1
Modes "1280x800"
EndSubSection
SubSection "Display"
Depth 4
Modes "1280x800"
EndSubSection
SubSection "Display"
Depth 8
Modes "1280x800"
EndSubSection
SubSection "Display"
Depth 15
Modes "1280x800"
EndSubSection
SubSection "Display"
Depth 16
Modes "1280x800"
EndSubSection
SubSection "Display"
Depth 24
Modes "1280x800"
EndSubSection
EndSection