Tive uma dificuldade tremenda para acertar esta questão e resolvi compartilha-la.
Máquina Positivo Ubuntu 8.04, Gnome 2.22.3
Placa de video ZOTAC (GeForce 7300 SE).
Monitores:
LG Flatron w1952TQ (LCD) 19"
LG ez T710BH (CRT) 17"
O xorg.conf ficou assim:
# xorg.conf (X.Org X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the xorg.conf manual page.
# (Type "man xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
# sudo dpkg-reconfigure -phigh xserver-xorg
# -------------------------------------------------------
# Teclado
# -------------------------------------------------------
Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "XkbRules" "xorg"
Option "XkbModel" "abnt2"
Option "XkbLayout" "br"
Option "XkbOptions" "lv3:ralt_switch"
EndSection
# -------------------------------------------------------
# Mouse
# -------------------------------------------------------
Section "InputDevice"
Identifier "Configured Mouse"
Driver "mouse"
Option "CorePointer"
EndSection
# -------------------------------------------------------
# Configuração do Monitor 0
# -------------------------------------------------------
Section "Device"
Identifier "Videocard0"
Boardname "nvidia"
Busid "PCI:1:0:0"
Driver "nvidia"
Screen 0
EndSection
#
Section "Monitor"
Identifier "Monitor0"
Vendorname "LG Electronics Inc."
Modelname "LG ez T710BH"
Horizsync 30.0-71.0
Vertrefresh 50.0-160.0
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 "640x480@85" 36.0 640 696 752 832 480 481 484 509 -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@85" 56.3 800 832 896 1048 600 601 604 631 +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@85" 94.5 1024 1072 1168 1376 768 769 772 808 +hsync +vsync
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 "1024x768@43" 44.9 1024 1032 1208 1264 768 768 776 817 +hsync interlace +vsync
modeline "1152x864@75" 108.0 1152 1216 1344 1600 864 865 868 900 +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 "1400x1050@60" 122.61 1400 1488 1640 1880 1050 1051 1054 1087 -hsync +vsync
Gamma 1.0
EndSection
#
Section "Screen"
Identifier "Screen0"
Monitor "Monitor0"
Device "Videocard0"
Defaultdepth 24
SubSection "Display"
Depth 24
Modes "1400x1050@60" "1280x1024@60" "1280x960@60" "1152x864@75" "1024x768@43" "1024x768@60" "1024x768@70" "1024x768@75" "1024x768@85" "832x624@75" "800x600@60" "800x600@85" "800x600@75" "800x600@72" "800x600@56" "640x480@85" "640x480@75" "640x480@72" "640x480@60"
EndSubSection
EndSection
# -------------------------------------------------------
# Configuração do Monitor 1
# -------------------------------------------------------
Section "device" #
Identifier "device1"
Boardname "nvidia"
Busid "PCI:1:0:0"
Driver "nvidia"
Screen 1
EndSection
#
Section "monitor" #
Identifier "monitor1"
Vendorname "LG Electronics Inc."
Modelname "LG L1952TQ (Digital)"
Horizsync 30.0-71.0
Vertrefresh 56.0-75.0
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 "1280x768@60" 80.14 1280 1344 1480 1680 768 769 772 795 -hsync +vsync
modeline "1280x720@60" 74.48 1280 1336 1472 1664 720 721 724 746 -hsync +vsync
modeline "1280x800@75" 107.21 1280 1360 1496 1712 800 801 804 835 -hsync +vsync
modeline "1280x768@75" 102.98 1280 1360 1496 1712 768 769 772 802 -hsync +vsync
modeline "1280x800@60" 83.46 1280 1344 1480 1680 800 801 804 828 -hsync +vsync
modeline "1440x900@75" 136.49 1440 1536 1688 1936 900 901 904 940 -hsync +vsync
modeline "1440x900@60" 106.47 1440 1520 1672 1904 900 901 904 932 -hsync +vsync
modeline "1600x1024@60" 136.36 1600 1704 1872 2144 1024 1025 1028 1060 -hsync +vsync
modeline "1680x1050@60" 147.14 1680 1784 1968 2256 1050 1051 1054 1087 -hsync +vsync
Gamma 1.0
EndSection
Section "screen" #
Identifier "screen1"
Device "device1"
Monitor "monitor1"
Defaultdepth 24
SubSection "Display"
Depth 24
Modes "1440x900@75" "1440x900@60" "1280x800@60" "1600x1024@60" "1280x768@75" "1680x1050@60" "1280x800@75" "1280x720@60" "1280x768@60" "800x600@60" "800x600@75" "800x600@72" "800x600@56"
EndSubSection
EndSection
#
# -------------------------------------------------------
# Layout dos monitores
# -------------------------------------------------------
Section "ServerLayout"
Identifier "Default Layout"
screen 0 "Screen0" 0 0
screen 1 "screen1" rightof "Screen0"
EndSection
Section "Module"
Load "glx"
EndSection
Section "ServerFlags"
Option "Xinerama" "true"
EndSection