Can also be configured through:

 sudo dpkg-reconfigure xserver-xorg

Remember to install 915resolution and configure /etc/default/915resolution. Put in what resolution you want. Get the parameters from:

915resolution -l
# /etc/X11/xorg.conf (xorg 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(5) 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

Section "Files"
        FontPath        "/usr/share/fonts/X11/misc"
        FontPath        "/usr/share/fonts/X11/cyrillic"
        FontPath        "/usr/share/fonts/X11/100dpi/:unscaled"
        FontPath        "/usr/share/fonts/X11/75dpi/:unscaled"
        FontPath        "/usr/share/fonts/X11/Type1"
        FontPath        "/usr/share/fonts/X11/100dpi"
        FontPath        "/usr/share/fonts/X11/75dpi"
        # path to defoma fonts
        FontPath        "/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
        Load    "bitmap"
        Load    "ddc"
        Load    "dri"
        Load    "extmod"
        Load    "freetype"
        Load    "glx"
        Load    "int10"
        Load    "vbe"
EndSection

Section "InputDevice"
        Identifier      "Generic Keyboard"
        Driver          "kbd"
        Option          "CoreKeyboard"
        Option          "XkbRules"      "xorg"
        Option          "XkbModel"      "pc105"
        Option          "XkbLayout"     "dk"
EndSection

Section "InputDevice"
        Identifier      "Configured Mouse"
        Driver          "mouse"
        Option          "CorePointer"
        Option          "Device"                "/dev/input/mice"
        Option          "Protocol"              "ExplorerPS/2"
        Option          "ZAxisMapping"          "4 5"
        Option          "Emulate3Buttons"       "true"
EndSection

Section "InputDevice"
        Driver          "wacom"
        Identifier      "stylus"
        Option          "Device"        "/dev/input/wacom"
        Option          "Type"          "stylus"
        Option          "ForceDevice"   "ISDV4"         # Tablet PC ONLY
EndSection

Section "InputDevice"
        Driver          "wacom"
        Identifier      "eraser"
        Option          "Device"        "/dev/input/wacom"
        Option          "Type"          "eraser"
        Option          "ForceDevice"   "ISDV4"         # Tablet PC ONLY
EndSection

Section "InputDevice"
        Driver          "wacom"
        Identifier      "cursor"
        Option          "Device"        "/dev/input/wacom"
        Option          "Type"          "cursor"
        Option          "ForceDevice"   "ISDV4"         # Tablet PC ONLY
EndSection

Section "Device"
        Identifier      "Intel Corporation 82915G/GV/910GL Integrated Graphics Controller"
        Driver          "i810"
        BusID           "PCI:0:2:0"
EndSection

Section "Monitor"
        Identifier      "Generic Monitor"
        Option          "DPMS"
        HorizSync       30-100
        VertRefresh     50-160
EndSection

Section "Screen"
        Identifier      "Default Screen"
        Device          "Intel Corporation 82915G/GV/910GL Integrated Graphics Controller"
        Monitor         "Generic Monitor"
        DefaultDepth    24
        SubSection "Display"
                Depth           1
                Modes           "1600x1200" "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           4
                Modes           "1600x1200" "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           8

                Modes           "1600x1200" "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           15
                Modes           "1600x1200" "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           16
                Modes           "1600x1200" "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           24
                Modes           "1600x1200" "1280x1024" "1024x768" "800x600" "640x480"
        EndSubSection
EndSection

Section "ServerLayout"
        Identifier      "Default Layout"
        Screen          "Default Screen"
        InputDevice     "Generic Keyboard"
        InputDevice     "Configured Mouse"
        InputDevice     "stylus"        "SendCoreEvents"
        InputDevice     "cursor"        "SendCoreEvents"
        InputDevice     "eraser"        "SendCoreEvents"
EndSection

Section "DRI"
        Mode    0666
EndSection
# /.../
# SaX generated X11 config file
# Created on: 2007-07-17T21:29:02+0200.
#
# Version: 8.1
# Contact: Marcus Schaefer <sax@suse.de>, 2005
# Contact: SaX-User list <https://lists.berlios.de/mailman/listinfo/sax-users>
#
# Automatically generated by [ISaX] (8.1)
# PLEASE DO NOT EDIT THIS FILE!
#
Section "Files"
  FontPath     "/usr/share/fonts/misc:unscaled"
  FontPath     "/usr/share/fonts/local"
  FontPath     "/usr/share/fonts/75dpi:unscaled"
  FontPath     "/usr/share/fonts/100dpi:unscaled"
  FontPath     "/usr/share/fonts/Type1"
  FontPath     "/usr/share/fonts/URW"
  FontPath     "/usr/share/fonts/Speedo"
  FontPath     "/usr/share/fonts/PEX"
  FontPath     "/usr/share/fonts/cyrillic"
  FontPath     "/usr/share/fonts/latin2/misc:unscaled"
  FontPath     "/usr/share/fonts/latin2/75dpi:unscaled"
  FontPath     "/usr/share/fonts/latin2/100dpi:unscaled"
  FontPath     "/usr/share/fonts/latin2/Type1"
  FontPath     "/usr/share/fonts/latin7/75dpi:unscaled"
  FontPath     "/usr/share/fonts/baekmuk:unscaled"
  FontPath     "/usr/share/fonts/japanese:unscaled"
  FontPath     "/usr/share/fonts/kwintv"
  FontPath     "/usr/share/fonts/truetype"
  FontPath     "/usr/share/fonts/uni:unscaled"
  FontPath     "/usr/share/fonts/CID"
  FontPath     "/usr/share/fonts/ucs/misc:unscaled"
  FontPath     "/usr/share/fonts/ucs/75dpi:unscaled"
  FontPath     "/usr/share/fonts/ucs/100dpi:unscaled"
  FontPath     "/usr/share/fonts/hellas/misc:unscaled"
  FontPath     "/usr/share/fonts/hellas/75dpi:unscaled"
  FontPath     "/usr/share/fonts/hellas/100dpi:unscaled"
  FontPath     "/usr/share/fonts/hellas/Type1"
  FontPath     "/usr/share/fonts/misc/sgi:unscaled"
  FontPath     "/usr/share/fonts/xtest"
  FontPath     "/opt/kde3/share/fonts"
  FontPath     "unix/:7100"
  InputDevices "/dev/gpmdata"
  InputDevices "/dev/input/mice"
EndSection

Section "ServerFlags"
  Option       "AllowMouseOpenFail" "on"
EndSection

Section "Module"
  Load         "dbe"
  Load         "type1"
  Load         "freetype"
  Load         "extmod"
  Load         "glx"
  Load         "v4l"
EndSection

Section "InputDevice"
  Driver       "kbd"
  Identifier   "Keyboard[0]"
  Option       "Protocol" "Standard"
  Option       "XkbLayout" "dk"
  Option       "XkbModel" "pc104"
  Option       "XkbRules" "xfree86"
EndSection

Section "InputDevice"
  Driver       "mouse"
  Identifier   "Mouse[1]"
  Option       "Buttons" "10"
  Option       "Device" "/dev/input/mice"
  Option       "Name" "Logitech USB Receiver"
  Option       "Protocol" "explorerps/2"
  Option       "Vendor" "Sysp"
  Option       "ZAxisMapping" "4 5"
EndSection

Section "Monitor"
  Option       "CalcAlgorithm" "XServerPool"
  DisplaySize  386 290
  HorizSync    30-110
  Identifier   "Monitor[0]"
  ModelName    "SYNCMASTER 950NF(T)"
  Option       "DPMS"
  VendorName   "SAMSUNG"
  VertRefresh  50-160
  UseModes     "Modes[0]"
EndSection

Section "Modes"
  Identifier   "Modes[0]"
  Modeline 	"800x600" 40.00 800 840 968 1056 600 601 605 628 +HSync +VSync
  Modeline 	"1280x1024" 157.50 1280 1344 1504 1728 1024 1025 1028 1072
EndSection

Section "Screen"
  DefaultDepth 24
  SubSection "Display"
    Depth      15
    Modes      "1280x1024" "1280x960" "1280x800" "1152x864" "1280x768" "1024x768" "1280x600" "1024x600" "800x600" "768x576" "640x480" 
  EndSubSection
  SubSection "Display"
    Depth      16
    Modes      "1280x1024" "1280x960" "1280x800" "1152x864" "1280x768" "1024x768" "1280x600" "1024x600" "800x600" "768x576" "640x480" 
  EndSubSection
  SubSection "Display"
    Depth      24
    Modes      "1280x1024" "1280x960" "1280x800" "1152x864" "1280x768" "1024x768" "1280x600" "1024x600" "800x600" "768x576" "640x480" 
  EndSubSection
  SubSection "Display"
    Depth      32
    Modes      "1280x1024" "1280x960" "1280x800" "1152x864" "1280x768" "1024x768" "1280x600" "1024x600" "800x600" "768x576" "640x480" 
  EndSubSection
  SubSection "Display"
    Depth      8
    Modes      "1280x1024" "1280x960" "1280x800" "1152x864" "1280x768" "1024x768" "1280x600" "1024x600" "800x600" "768x576" "640x480" 
  EndSubSection
  Device       "Device[0]"
  Identifier   "Screen[0]"
  Monitor      "Monitor[0]"
EndSection

Section "Device"
  BoardName    "915 G"
  BusID        "0:2:0"
  Driver       "i810"
  Identifier   "Device[0]"
  Option       "NoDDC"
  VendorName   "Intel"
EndSection

Section "ServerLayout"
  Identifier   "Layout[all]"
  InputDevice  "Keyboard[0]" "CoreKeyboard"
  InputDevice  "Mouse[1]" "CorePointer"
  Option       "Clone" "off"
  Option       "Xinerama" "off"
  Screen       "Screen[0]"
EndSection

Section "DRI"
    Group      "video"
    Mode       0660
EndSection

Section "Extensions"
EndSection

My xorg.conf on Hardy Heron: :howtos:xorg.conf