ATI ES1000 515E and a widescreen monitor

The ATI ES1000 is the built-in PCI graphics card in a Dell PowerEdge SC440, and I have it hooked up to a Samsung SyncMaster 205BW, capable of doing 1680x1050.

To see which card you have:
lscpi | grep VGA
The output I get:
05:07.0 VGA compatible controller: ATI Technologies Inc ES1000 (rev 02)
(lspci is part of the pciutils package)

For a Fedora 8 x86_64 installation, all I did was add these two lines
Modes "1680x1050"
Virtual 1680 1050
to the Display subsection of the Screen section.

Note: I just (Feb 2008) updated some packages on this system, after which the widescreen stopped working :-(.
Just now (March 2008) got it working again: change the DefaultDepth and Depth values in the Screen section of your xorg.conf from 24 to 16... (the driver is suddenly picky about the maximum clock speed of the graphics card (/var/log/Xorg.0.log says Not using default mode "1680x1050" (bad mode clock/interlace/doublescan)). My xorg and ATI driver versions:
xorg-x11-server-Xorg-1.3.0.0-42
xorg-x11-drv-ati-6.8.0.1

For a Fedora 7 installation I used the xorg.conf file below: Fortunately I already had a working xorg.conf for an nVidia card, which I could use with a few minor changes (see below). Note that the settings for your input devices may be a bit different. You could try to run:
X -configure
first, and then modify the resulting xorg.conf.new file (and save it as /etc/X11/xorg.conf).

Section "ServerLayout"
  Identifier   "single"
  Screen     0 "SingleScreen" 0 0
  InputDevice   "Mouse0" "CorePointer"
  InputDevice   "Keyboard0" "CoreKeyboard"
EndSection

Section "Device"
  Identifier "ES1000"
  VendorName "ATI"
   Driver "radeon"
EndSection

Section "Monitor"
  Identifier "Monitor0"
  VendorName "Samsung"
  ModelName "205BW"
  HorizSync 30.0 - 81.0
  VertRefresh 56.0 - 75.0
EndSection

Section "Screen"
  Identifier  "SingleScreen"
  Device   "ES1000"
  Monitor   "Monitor0"
  DefaultDepth 16
  Subsection "Display"
       Depth   16
    Modes "1680x1050"
  EndSubsection
EndSection

Section "Files"
  RgbPath   "/usr/X11R6/lib/X11/rgb"
  FontPath   "unix/:7100"
EndSection

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

Section "InputDevice"
  Identifier  "Keyboard0"
  Driver   "kbd"
  Option     "XkbModel" "pc105"
  Option     "XkbLayout" "us"
EndSection

Section "InputDevice"
  Identifier   "Mouse0"
  Driver   "mouse"
  Option     "Protocol" "IMPS/2"
  Option     "Device" "/dev/input/mice"
  Option     "ZAxisMapping" "4 5"
  Option     "Emulate3Buttons" "yes"
EndSection