Quando minha antiga placa mâe queimou e eu tive que comprar outra tive bastante problemas em achar a configuração certa para meu Ubuntu.
depois de muito teste consegui! e vim aqui compartilhar :)

Modelo da Placa: MB Intel DG31PR /Core Quad/CORE2/Dual Core/CEL/LGA775/DD2 667/ 800MHZ/FSB 1333 MHz/ a/v/r - BOX
Vídeo Subsistema de gráficos integrados Intel® Graphics Media Accelerator 950
Monitor: LG FLATRON L1753T-SF

xorg.conf
[source language="ruby"]

# xorg.conf (X.Org X Window System server configuration file)
#
# This file was generated by failsafeDexconf, using
# values from the debconf database and some overrides to use vesa mode.
#
# You should use dexconf or another such tool for creating a "real" xorg.conf
# For example:
#   sudo dpkg-reconfigure -phigh xserver-xorg
Section "InputDevice"
 Identifier    "Generic Keyboard"
 Driver        "kbd"
 Option        "XkbRules"    "xorg"
 Option        "XkbModel"    "pc105"
 Option        "XkbLayout"    "pt"
 Option        "XkbOptions"    "lv3:ralt_switch"
EndSection

Section "InputDevice"
 Identifier    "Configured Mouse"
 Driver        "mouse"
EndSection

Section "Device"
 Identifier    "Configured Video Device"
 Boardname    "vesa"
 Busid        "PCI:0:2:0"
 Driver        "intel"
 Screen    0
EndSection

Section "Monitor"
 Identifier    "Configured Monitor"
 Vendorname    "LG Electronics Inc."
 Modelname    "LG L1760TG (Analog)"
 Horizsync    30.0-83.0
 Vertrefresh    56.0-75.0
 modeline  "640x480@60" 25.2 640 656 752 800 480 490 492 525 -vsync -hsync
 modeline  "640x480@72" 31.5 640 664 704 832 480 489 491 520 -vsync -hsync
 modeline  "640x480@75" 31.5 640 656 720 840 480 481 484 500 -vsync -hsync
 modeline  "800x600@56" 36.0 800 824 896 1024 600 601 603 625 +hsync +vsync
 modeline  "800x600@72" 50.0 800 856 976 1040 600 637 643 666 +hsync +vsync
 modeline  "800x600@75" 49.5 800 816 896 1056 600 601 604 625 +hsync +vsync
 modeline  "800x600@60" 40.0 800 840 968 1056 600 601 605 628 +hsync +vsync
 modeline  "832x624@75" 57.284 832 864 928 1152 624 625 628 667 -vsync -hsync
 modeline  "1024x768@75" 78.8 1024 1040 1136 1312 768 769 772 800 +hsync +vsync
 modeline  "1024x768@70" 75.0 1024 1048 1184 1328 768 771 777 806 -vsync -hsync
 modeline  "1024x768@60" 65.0 1024 1048 1184 1344 768 771 777 806 -vsync -hsync
 modeline  "1152x864@75" 108.0 1152 1216 1344 1600 864 865 868 900 +hsync +vsync
 modeline  "1280x1024@75" 135.0 1280 1296 1440 1688 1024 1025 1028 1066 +hsync +vsync
 modeline  "1280x960@60" 102.1 1280 1360 1496 1712 960 961 964 994 -hsync +vsync
 modeline  "1280x1024@60" 108.0 1280 1328 1440 1688 1024 1025 1028 1066 +hsync +vsync
 modeline  "1280x960@75" 129.86 1280 1368 1504 1728 960 961 964 1002 -hsync +vsync
 modeline  "1400x1050@60" 122.61 1400 1488 1640 1880 1050 1051 1054 1087 -hsync +vsync
 modeline  "1400x1050@75" 155.85 1400 1496 1648 1896 1050 1051 1054 1096 -hsync +vsync
 modeline  "1600x1200@65" 175.5 1600 1664 1856 2160 1200 1201 1204 1250 +hsync +vsync
 modeline  "1600x1200@60" 162.0 1600 1664 1856 2160 1200 1201 1204 1250 +hsync +vsync
 modeline  "1792x1344@60" 204.8 1792 1920 2120 2448 1344 1345 1348 1394 -hsync +vsync
 Gamma    1.0
EndSection

Section "Screen"
 Identifier    "Default Screen"
 Device        "Configured Video Device"
 Monitor        "Configured Monitor"
 Defaultdepth    24
 SubSection "Display"
 Depth    24
 Virtual    1792    1344
 Modes        "1024x768@75"    "1024x768@70"    "832x624@75"    "1024x768@60"    "800x600@60"    "1152x864@75"    "800x600@75"    "1280x1024@75"    "800x600@72"    "1280x960@60"    "800x600@56"    "1280x1024@60"    "640x480@75"    "1280x960@75"    "640x480@72"    "1400x1050@60"    "640x480@60"    "1400x1050@75"    "1600x1200@65"    "1600x1200@60"    "1792x1344@60"
 EndSubSection
EndSection

Section "ServerLayout"
 Identifier    "Default Layout"
 screen 0 "Default Screen" 0 0
EndSection
Section "Module"
 Load        "glx"
 Load        "GLcore"
 Load        "v4l"
EndSection
Section "ServerFlags"
EndSection

[/source]

Bom pra mim funcionou beleza. abraços!